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 $196.33   8.554%   $213.1241   $213.12   $213.10   $213.10  
  Purchase #2 $204.65   6.196%   $217.3301   $217.33   $217.35   $217.30  
  Purchase #3 $12.72   13.456%   $14.4316   $14.43   $14.45   $14.40  
  Purchase #4 $159.71   6.412%   $169.9506   $169.95   $169.95   $170.00  
  Purchase #5 $5.38   4.331%   $5.613   $5.61   $5.60   $5.60  
  Purchase #6 $126.25   5.117%   $132.7102   $132.71   $132.70   $132.70  
  Purchase #7 $143.48   6.828%   $153.2768   $153.28   $153.30   $153.30  
  7 purchase totals = $848.52       $906.4364   $906.43   $906.45   $906.40