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 $177.57   13.855%   $202.1723   $202.17   $202.15   $202.20  
  Purchase #2 $208.55   7.578%   $224.3539   $224.35   $224.35   $224.40  
  Purchase #3 $10.62   11.773%   $11.8703   $11.87   $11.85   $11.90  
  Purchase #4 $54.64   10.443%   $60.3461   $60.35   $60.35   $60.30  
  Purchase #5 $215.65   11.864%   $241.2347   $241.23   $241.25   $241.20  
  Purchase #6 $18.42   3.160%   $19.0021   $19.00   $19.00   $19.00  
  Purchase #7 $40.38   4.409%   $42.1604   $42.16   $42.15   $42.20  
  7 purchase totals = $725.83       $801.1398   $801.13   $801.10   $801.20