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 $41.45   6.307%   $44.0643   $44.06   $44.05   $44.10  
  Purchase #2 $205.93   5.535%   $217.3282   $217.33   $217.35   $217.30  
  Purchase #3 $16.86   11.599%   $18.8156   $18.82   $18.80   $18.80  
  Purchase #4 $33.47   4.416%   $34.948   $34.95   $34.95   $34.90  
  Purchase #5 $130.66   8.232%   $141.4159   $141.42   $141.40   $141.40  
  Purchase #6 $212.70   7.738%   $229.1587   $229.16   $229.15   $229.20  
  Purchase #7 $139.65   11.780%   $156.1008   $156.10   $156.10   $156.10  
  7 purchase totals = $780.72       $841.8315   $841.84   $841.80   $841.80