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 $54.71   9.684%   $60.0081   $60.01   $60.00   $60.00  
  Purchase #2 $106.93   12.332%   $120.1166   $120.12   $120.10   $120.10  
  Purchase #3 $16.25   9.622%   $17.8136   $17.81   $17.80   $17.80  
  Purchase #4 $147.93   7.124%   $158.4685   $158.47   $158.45   $158.50  
  Purchase #5 $244.62   5.516%   $258.1132   $258.11   $258.10   $258.10  
  Purchase #6 $163.85   11.203%   $182.2061   $182.21   $182.20   $182.20  
  Purchase #7 $189.52   6.441%   $201.727   $201.73   $201.75   $201.70  
  7 purchase totals = $923.81       $998.4531   $998.46   $998.40   $998.40