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 $96.35   6.501%   $102.6137   $102.61   $102.60   $102.60  
  Purchase #2 $216.60   3.250%   $223.6395   $223.64   $223.65   $223.60  
  Purchase #3 $208.90   12.808%   $235.6559   $235.66   $235.65   $235.70  
  Purchase #4 $85.65   13.648%   $97.3395   $97.34   $97.35   $97.30  
  Purchase #5 $65.32   8.486%   $70.8631   $70.86   $70.85   $70.90  
  Purchase #6 $43.62   13.422%   $49.4747   $49.47   $49.45   $49.50  
  Purchase #7 $150.63   9.397%   $164.7847   $164.78   $164.80   $164.80  
  7 purchase totals = $867.07       $944.3711   $944.36   $944.35   $944.40