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 $188.34   9.195%   $205.6579   $205.66   $205.65   $205.70  
  Purchase #2 $180.41   8.395%   $195.5554   $195.56   $195.55   $195.60  
  Purchase #3 $84.30   11.742%   $94.1985   $94.20   $94.20   $94.20  
  Purchase #4 $118.29   11.224%   $131.5669   $131.57   $131.55   $131.60  
  Purchase #5 $39.98   8.685%   $43.4523   $43.45   $43.45   $43.50  
  Purchase #6 $127.80   10.327%   $140.9979   $141.00   $141.00   $141.00  
  Purchase #7 $184.29   13.829%   $209.7755   $209.78   $209.80   $209.80  
  7 purchase totals = $923.41       $1,021.2044   $1,021.22   $1,021.20   $1,021.40