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 $59.61   8.268%   $64.5386   $64.54   $64.55   $64.50  
  Purchase #2 $205.93   12.492%   $231.6548   $231.65   $231.65   $231.70  
  Purchase #3 $194.75   3.409%   $201.389   $201.39   $201.40   $201.40  
  Purchase #4 $191.43   11.358%   $213.1726   $213.17   $213.15   $213.20  
  Purchase #5 $116.80   13.165%   $132.1767   $132.18   $132.20   $132.20  
  Purchase #6 $150.63   3.463%   $155.8463   $155.85   $155.85   $155.80  
  Purchase #7 $18.56   6.309%   $19.731   $19.73   $19.75   $19.70  
  7 purchase totals = $937.71       $1,018.5090   $1,018.51   $1,018.55   $1,018.50