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 $222.89   9.497%   $244.0579   $244.06   $244.05   $244.10  
  Purchase #2 $181.99   13.174%   $205.9654   $205.97   $205.95   $206.00  
  Purchase #3 $61.73   4.585%   $64.5603   $64.56   $64.55   $64.60  
  Purchase #4 $113.46   8.448%   $123.0451   $123.05   $123.05   $123.00  
  Purchase #5 $136.54   4.435%   $142.5955   $142.60   $142.60   $142.60  
  Purchase #6 $162.43   12.162%   $182.1847   $182.18   $182.20   $182.20  
  Purchase #7 $27.51   7.331%   $29.5268   $29.53   $29.55   $29.50  
  7 purchase totals = $906.55       $991.9357   $991.95   $991.95   $992.00