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 $224.94   11.664%   $251.177   $251.18   $251.20   $251.20  
  Purchase #2 $119.58   4.103%   $124.4864   $124.49   $124.50   $124.50  
  Purchase #3 $116.67   4.539%   $121.9657   $121.97   $121.95   $122.00  
  Purchase #4 $183.69   6.768%   $196.1221   $196.12   $196.10   $196.10  
  Purchase #5 $114.47   7.638%   $123.2132   $123.21   $123.20   $123.20  
  Purchase #6 $79.94   10.518%   $88.3481   $88.35   $88.35   $88.30  
  Purchase #7 $205.62   7.644%   $221.3376   $221.34   $221.35   $221.30  
  7 purchase totals = $1,044.91       $1,126.6501   $1,126.66   $1,126.65   $1,126.60