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 $163.35   13.821%   $185.9266   $185.93   $185.95   $185.90  
  Purchase #2 $245.69   13.558%   $279.0007   $279.00   $279.00   $279.00  
  Purchase #3 $213.42   10.550%   $235.9358   $235.94   $235.95   $235.90  
  Purchase #4 $235.97   12.167%   $264.6805   $264.68   $264.70   $264.70  
  Purchase #5 $212.32   10.537%   $234.6922   $234.69   $234.70   $234.70  
  Purchase #6 $87.79   12.561%   $98.8173   $98.82   $98.80   $98.80  
  Purchase #7 $169.73   4.637%   $177.6004   $177.60   $177.60   $177.60  
  7 purchase totals = $1,328.27       $1,476.6535   $1,476.66   $1,476.70   $1,476.60