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 $134.84   10.534%   $149.044   $149.04   $149.05   $149.00  
  Purchase #2 $58.58   5.451%   $61.7732   $61.77   $61.75   $61.80  
  Purchase #3 $72.29   9.817%   $79.3867   $79.39   $79.40   $79.40  
  Purchase #4 $157.51   5.838%   $166.7054   $166.71   $166.70   $166.70  
  Purchase #5 $86.82   11.372%   $96.6932   $96.69   $96.70   $96.70  
  Purchase #6 $103.52   10.512%   $114.402   $114.40   $114.40   $114.40  
  Purchase #7 $167.67   5.543%   $176.9639   $176.96   $176.95   $177.00  
  7 purchase totals = $781.23       $844.9684   $844.96   $844.95   $845.00