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 $68.51   11.540%   $76.4161   $76.42   $76.40   $76.40  
  Purchase #2 $141.70   13.317%   $160.5702   $160.57   $160.55   $160.60  
  Purchase #3 $37.38   5.137%   $39.3002   $39.30   $39.30   $39.30  
  Purchase #4 $181.75   8.549%   $197.2878   $197.29   $197.30   $197.30  
  Purchase #5 $88.44   3.245%   $91.3099   $91.31   $91.30   $91.30  
  Purchase #6 $83.64   10.869%   $92.7308   $92.73   $92.75   $92.70  
  Purchase #7 $159.93   4.758%   $167.5395   $167.54   $167.55   $167.50  
  7 purchase totals = $761.35       $825.1545   $825.16   $825.15   $825.10