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 $151.93   12.526%   $170.9608   $170.96   $170.95   $171.00  
  Purchase #2 $244.70   7.514%   $263.0868   $263.09   $263.10   $263.10  
  Purchase #3 $118.91   9.259%   $129.9199   $129.92   $129.90   $129.90  
  Purchase #4 $26.37   12.526%   $29.6731   $29.67   $29.65   $29.70  
  Purchase #5 $136.29   11.669%   $152.1937   $152.19   $152.20   $152.20  
  Purchase #6 $153.26   10.649%   $169.5807   $169.58   $169.60   $169.60  
  Purchase #7 $110.35   8.285%   $119.4925   $119.49   $119.50   $119.50  
  7 purchase totals = $941.81       $1,034.9075   $1,034.90   $1,034.90   $1,035.00