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 $91.97   5.114%   $96.6733   $96.67   $96.65   $96.70  
  Purchase #2 $9.85   9.640%   $10.7995   $10.80   $10.80   $10.80  
  Purchase #3 $115.97   5.112%   $121.8984   $121.90   $121.90   $121.90  
  Purchase #4 $48.89   11.611%   $54.5666   $54.57   $54.55   $54.60  
  Purchase #5 $117.51   5.849%   $124.3832   $124.38   $124.40   $124.40  
  Purchase #6 $151.61   6.611%   $161.6329   $161.63   $161.65   $161.60  
  Purchase #7 $174.76   4.848%   $183.2324   $183.23   $183.25   $183.20  
  7 purchase totals = $710.56       $753.1863   $753.18   $753.20   $753.20