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 $165.54   11.377%   $184.3735   $184.37   $184.35   $184.40  
  Purchase #2 $207.75   6.607%   $221.476   $221.48   $221.50   $221.50  
  Purchase #3 $24.45   5.473%   $25.7881   $25.79   $25.80   $25.80  
  Purchase #4 $59.94   4.484%   $62.6277   $62.63   $62.65   $62.60  
  Purchase #5 $205.83   3.773%   $213.596   $213.60   $213.60   $213.60  
  Purchase #6 $35.55   4.525%   $37.1586   $37.16   $37.15   $37.20  
  Purchase #7 $8.97   3.329%   $9.2686   $9.27   $9.25   $9.30  
  7 purchase totals = $708.03       $754.2885   $754.30   $754.30   $754.40