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 $35.46   5.170%   $37.2933   $37.29   $37.30   $37.30  
  Purchase #2 $176.76   10.528%   $195.3693   $195.37   $195.35   $195.40  
  Purchase #3 $167.67   9.119%   $182.9598   $182.96   $182.95   $183.00  
  Purchase #4 $52.77   11.854%   $59.0254   $59.03   $59.05   $59.00  
  Purchase #5 $166.60   10.177%   $183.5549   $183.55   $183.55   $183.60  
  Purchase #6 $91.96   7.134%   $98.5204   $98.52   $98.50   $98.50  
  Purchase #7 $212.73   6.228%   $225.9788   $225.98   $226.00   $226.00  
  7 purchase totals = $903.95       $982.7019   $982.70   $982.70   $982.80