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 $186.51   8.285%   $201.9624   $201.96   $201.95   $202.00  
  Purchase #2 $111.51   10.633%   $123.3669   $123.37   $123.35   $123.40  
  Purchase #3 $174.54   7.464%   $187.5677   $187.57   $187.55   $187.60  
  Purchase #4 $226.59   5.666%   $239.4286   $239.43   $239.45   $239.40  
  Purchase #5 $181.34   11.222%   $201.69   $201.69   $201.70   $201.70  
  Purchase #6 $161.54   7.196%   $173.1644   $173.16   $173.15   $173.20  
  Purchase #7 $64.98   12.662%   $73.2078   $73.21   $73.20   $73.20  
  7 purchase totals = $1,107.01       $1,200.3878   $1,200.39   $1,200.35   $1,200.50