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 $85.79   12.131%   $96.1972   $96.20   $96.20   $96.20  
  Purchase #2 $11.40   9.137%   $12.4416   $12.44   $12.45   $12.40  
  Purchase #3 $17.93   12.647%   $20.1976   $20.20   $20.20   $20.20  
  Purchase #4 $164.37   9.170%   $179.4427   $179.44   $179.45   $179.40  
  Purchase #5 $134.64   11.738%   $150.444   $150.44   $150.45   $150.40  
  Purchase #6 $193.92   3.735%   $201.1629   $201.16   $201.15   $201.20  
  Purchase #7 $243.79   7.256%   $261.4794   $261.48   $261.50   $261.50  
  7 purchase totals = $851.84       $921.3654   $921.36   $921.40   $921.30