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 $105.48   12.494%   $118.6587   $118.66   $118.65   $118.70  
  Purchase #2 $112.33   8.559%   $121.9443   $121.94   $121.95   $121.90  
  Purchase #3 $37.49   9.350%   $40.9953   $41.00   $41.00   $41.00  
  Purchase #4 $43.54   4.305%   $45.4144   $45.41   $45.40   $45.40  
  Purchase #5 $230.92   11.729%   $258.0046   $258.00   $258.00   $258.00  
  Purchase #6 $49.74   8.874%   $54.1539   $54.15   $54.15   $54.20  
  Purchase #7 $42.38   11.497%   $47.2524   $47.25   $47.25   $47.30  
  7 purchase totals = $621.88       $686.4236   $686.41   $686.40   $686.50