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 $7.56   3.873%   $7.8528   $7.85   $7.85   $7.90  
  Purchase #2 $141.68   11.379%   $157.8018   $157.80   $157.80   $157.80  
  Purchase #3 $54.74   13.126%   $61.9252   $61.93   $61.95   $61.90  
  Purchase #4 $39.81   10.175%   $43.8607   $43.86   $43.85   $43.90  
  Purchase #5 $43.49   7.641%   $46.8131   $46.81   $46.80   $46.80  
  Purchase #6 $35.74   9.733%   $39.2186   $39.22   $39.20   $39.20  
  Purchase #7 $133.53   5.344%   $140.6658   $140.67   $140.65   $140.70  
  7 purchase totals = $456.55       $498.1380   $498.14   $498.10   $498.20