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 $57.47   9.777%   $63.0888   $63.09   $63.10   $63.10  
  Purchase #2 $173.73   7.274%   $186.3671   $186.37   $186.35   $186.40  
  Purchase #3 $170.36   10.314%   $187.9309   $187.93   $187.95   $187.90  
  Purchase #4 $123.79   13.406%   $140.3853   $140.39   $140.40   $140.40  
  Purchase #5 $57.72   3.226%   $59.582   $59.58   $59.60   $59.60  
  Purchase #6 $42.43   9.217%   $46.3408   $46.34   $46.35   $46.30  
  Purchase #7 $182.89   11.658%   $204.2113   $204.21   $204.20   $204.20  
  7 purchase totals = $808.39       $887.9062   $887.91   $887.95   $887.90