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 $56.65   10.229%   $62.4447   $62.44   $62.45   $62.40  
  Purchase #2 $106.51   11.689%   $118.96   $118.96   $118.95   $119.00  
  Purchase #3 $135.53   13.110%   $153.298   $153.30   $153.30   $153.30  
  Purchase #4 $197.80   9.657%   $216.9015   $216.90   $216.90   $216.90  
  Purchase #5 $82.86   4.695%   $86.7503   $86.75   $86.75   $86.80  
  Purchase #6 $194.65   8.289%   $210.7845   $210.78   $210.80   $210.80  
  Purchase #7 $144.71   10.634%   $160.0985   $160.10   $160.10   $160.10  
  7 purchase totals = $918.71       $1,009.2375   $1,009.23   $1,009.25   $1,009.30