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 $188.25   3.534%   $194.9028   $194.90   $194.90   $194.90  
  Purchase #2 $165.92   6.793%   $177.1909   $177.19   $177.20   $177.20  
  Purchase #3 $166.85   12.343%   $187.4443   $187.44   $187.45   $187.40  
  Purchase #4 $236.77   5.129%   $248.9139   $248.91   $248.90   $248.90  
  Purchase #5 $197.87   8.319%   $214.3308   $214.33   $214.35   $214.30  
  Purchase #6 $186.94   4.671%   $195.672   $195.67   $195.65   $195.70  
  Purchase #7 $125.53   7.824%   $135.3515   $135.35   $135.35   $135.40  
  7 purchase totals = $1,268.13       $1,353.8062   $1,353.79   $1,353.80   $1,353.80