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 $114.81   8.740%   $124.8444   $124.84   $124.85   $124.80  
  Purchase #2 $194.90   11.213%   $216.7541   $216.75   $216.75   $216.80  
  Purchase #3 $169.74   9.192%   $185.3425   $185.34   $185.35   $185.30  
  Purchase #4 $56.92   5.735%   $60.1844   $60.18   $60.20   $60.20  
  Purchase #5 $232.26   6.758%   $247.9561   $247.96   $247.95   $248.00  
  Purchase #6 $105.92   8.810%   $115.2516   $115.25   $115.25   $115.30  
  Purchase #7 $86.81   7.532%   $93.3485   $93.35   $93.35   $93.30  
  7 purchase totals = $961.36       $1,043.6816   $1,043.67   $1,043.70   $1,043.70