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 $209.56   4.757%   $219.5288   $219.53   $219.55   $219.50  
  Purchase #2 $32.48   5.404%   $34.2352   $34.24   $34.25   $34.20  
  Purchase #3 $49.31   6.427%   $52.4792   $52.48   $52.50   $52.50  
  Purchase #4 $71.82   6.442%   $76.4466   $76.45   $76.45   $76.40  
  Purchase #5 $97.27   10.282%   $107.2713   $107.27   $107.25   $107.30  
  Purchase #6 $200.77   8.145%   $217.1227   $217.12   $217.10   $217.10  
  Purchase #7 $238.98   13.210%   $270.5493   $270.55   $270.55   $270.50  
  7 purchase totals = $900.19       $977.6331   $977.64   $977.65   $977.50