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 $61.56   7.179%   $65.9794   $65.98   $66.00   $66.00  
  Purchase #2 $111.29   9.579%   $121.9505   $121.95   $121.95   $122.00  
  Purchase #3 $33.90   13.824%   $38.5863   $38.59   $38.60   $38.60  
  Purchase #4 $13.92   12.715%   $15.6899   $15.69   $15.70   $15.70  
  Purchase #5 $231.92   8.429%   $251.4685   $251.47   $251.45   $251.50  
  Purchase #6 $164.25   11.593%   $183.2915   $183.29   $183.30   $183.30  
  Purchase #7 $33.44   9.289%   $36.5462   $36.55   $36.55   $36.50  
  7 purchase totals = $650.28       $713.5123   $713.52   $713.55   $713.60