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 $86.98   6.190%   $92.3641   $92.36   $92.35   $92.40  
  Purchase #2 $142.70   11.168%   $158.6367   $158.64   $158.65   $158.60  
  Purchase #3 $130.71   13.777%   $148.7179   $148.72   $148.70   $148.70  
  Purchase #4 $224.97   3.323%   $232.4458   $232.45   $232.45   $232.40  
  Purchase #5 $15.94   3.789%   $16.544   $16.54   $16.55   $16.50  
  Purchase #6 $229.50   8.697%   $249.4596   $249.46   $249.45   $249.50  
  Purchase #7 $219.47   10.870%   $243.3264   $243.33   $243.35   $243.30  
  7 purchase totals = $1,050.27       $1,141.4945   $1,141.50   $1,141.50   $1,141.40