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 $62.93   3.471%   $65.1143   $65.11   $65.10   $65.10  
  Purchase #2 $235.76   6.552%   $251.207   $251.21   $251.20   $251.20  
  Purchase #3 $27.58   5.775%   $29.1727   $29.17   $29.15   $29.20  
  Purchase #4 $24.76   5.303%   $26.073   $26.07   $26.05   $26.10  
  Purchase #5 $87.45   11.493%   $97.5006   $97.50   $97.50   $97.50  
  Purchase #6 $92.72   5.376%   $97.7046   $97.70   $97.70   $97.70  
  Purchase #7 $231.43   3.872%   $240.391   $240.39   $240.40   $240.40  
  7 purchase totals = $762.63       $807.1632   $807.15   $807.10   $807.20