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 $51.91   13.492%   $58.9137   $58.91   $58.90   $58.90  
  Purchase #2 $206.82   7.475%   $222.2798   $222.28   $222.30   $222.30  
  Purchase #3 $96.56   13.255%   $109.359   $109.36   $109.35   $109.40  
  Purchase #4 $39.38   5.598%   $41.5845   $41.58   $41.60   $41.60  
  Purchase #5 $114.60   4.867%   $120.1776   $120.18   $120.20   $120.20  
  Purchase #6 $213.67   10.112%   $235.2763   $235.28   $235.30   $235.30  
  Purchase #7 $151.72   12.577%   $170.8018   $170.80   $170.80   $170.80  
  7 purchase totals = $874.66       $958.3927   $958.39   $958.45   $958.50