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 $68.53   6.383%   $72.9043   $72.90   $72.90   $72.90  
  Purchase #2 $107.97   5.539%   $113.9505   $113.95   $113.95   $114.00  
  Purchase #3 $187.97   4.858%   $197.1016   $197.10   $197.10   $197.10  
  Purchase #4 $95.62   11.561%   $106.6746   $106.67   $106.65   $106.70  
  Purchase #5 $53.78   4.549%   $56.2265   $56.23   $56.25   $56.20  
  Purchase #6 $7.76   12.428%   $8.7244   $8.72   $8.70   $8.70  
  Purchase #7 $99.47   7.375%   $106.8059   $106.81   $106.80   $106.80  
  7 purchase totals = $621.10       $662.3878   $662.38   $662.35   $662.40