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 $51.73   13.761%   $58.8486   $58.85   $58.85   $58.80  
  Purchase #2 $234.93   8.826%   $255.6649   $255.66   $255.65   $255.70  
  Purchase #3 $229.40   8.828%   $249.6514   $249.65   $249.65   $249.70  
  Purchase #4 $66.45   5.443%   $70.0669   $70.07   $70.05   $70.10  
  Purchase #5 $201.37   13.635%   $228.8268   $228.83   $228.85   $228.80  
  Purchase #6 $43.32   10.359%   $47.8075   $47.81   $47.80   $47.80  
  Purchase #7 $85.99   12.201%   $96.4816   $96.48   $96.50   $96.50  
  7 purchase totals = $913.19       $1,007.3477   $1,007.35   $1,007.35   $1,007.40