Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $216.91   13.162%   $245.4597   $245.46   $245.45   $245.50  
  Purchase #2 $152.81   10.218%   $168.4241   $168.42   $168.40   $168.40  
  Purchase #3 $147.68   13.385%   $167.447   $167.45   $167.45   $167.40  
  Purchase #4 $167.67   9.118%   $182.9582   $182.96   $182.95   $183.00  
  Purchase #5 $200.57   12.691%   $226.0243   $226.02   $226.00   $226.00  
  Purchase #6 $123.29   5.506%   $130.0783   $130.08   $130.10   $130.10  
  Purchase #7 $172.27   6.214%   $182.9749   $182.97   $182.95   $183.00  
  7 purchase totals = $1,181.20       $1,303.3665   $1,303.36   $1,303.30   $1,303.40