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 $47.40   13.770%   $53.927   $53.93   $53.95   $53.90  
  Purchase #2 $56.77   12.422%   $63.822   $63.82   $63.80   $63.80  
  Purchase #3 $222.91   10.816%   $247.0199   $247.02   $247.00   $247.00  
  Purchase #4 $171.81   10.535%   $189.9102   $189.91   $189.90   $189.90  
  Purchase #5 $173.56   13.729%   $197.3881   $197.39   $197.40   $197.40  
  Purchase #6 $65.78   10.547%   $72.7178   $72.72   $72.70   $72.70  
  Purchase #7 $126.73   11.152%   $140.8629   $140.86   $140.85   $140.90  
  7 purchase totals = $864.96       $965.6479   $965.65   $965.60   $965.60