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 $245.90   12.678%   $277.0752   $277.08   $277.10   $277.10  
  Purchase #2 $213.59   12.107%   $239.4493   $239.45   $239.45   $239.40  
  Purchase #3 $236.48   9.856%   $259.7875   $259.79   $259.80   $259.80  
  Purchase #4 $172.69   3.724%   $179.121   $179.12   $179.10   $179.10  
  Purchase #5 $209.75   8.382%   $227.3312   $227.33   $227.35   $227.30  
  Purchase #6 $85.79   7.234%   $91.996   $92.00   $92.00   $92.00  
  Purchase #7 $178.37   6.710%   $190.3386   $190.34   $190.35   $190.30  
  7 purchase totals = $1,342.57       $1,465.0988   $1,465.11   $1,465.15   $1,465.00