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 $118.40   6.568%   $126.1765   $126.18   $126.20   $126.20  
  Purchase #2 $183.52   11.327%   $204.3073   $204.31   $204.30   $204.30  
  Purchase #3 $102.29   11.767%   $114.3265   $114.33   $114.35   $114.30  
  Purchase #4 $197.48   10.149%   $217.5222   $217.52   $217.50   $217.50  
  Purchase #5 $142.27   6.813%   $151.9629   $151.96   $151.95   $152.00  
  Purchase #6 $236.63   8.589%   $256.9542   $256.95   $256.95   $257.00  
  Purchase #7 $11.68   11.584%   $13.033   $13.03   $13.05   $13.00  
  7 purchase totals = $992.27       $1,084.2826   $1,084.28   $1,084.30   $1,084.30