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 $195.48   5.363%   $205.9636   $205.96   $205.95   $206.00  
  Purchase #2 $102.84   4.343%   $107.3063   $107.31   $107.30   $107.30  
  Purchase #3 $148.75   6.375%   $158.2328   $158.23   $158.25   $158.20  
  Purchase #4 $32.74   3.207%   $33.79   $33.79   $33.80   $33.80  
  Purchase #5 $143.86   10.617%   $159.1336   $159.13   $159.15   $159.10  
  Purchase #6 $41.52   13.764%   $47.2348   $47.23   $47.25   $47.20  
  Purchase #7 $59.71   10.724%   $66.1133   $66.11   $66.10   $66.10  
  7 purchase totals = $724.90       $777.7744   $777.76   $777.80   $777.70