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 $57.53   8.436%   $62.3832   $62.38   $62.40   $62.40  
  Purchase #2 $46.70   13.195%   $52.8621   $52.86   $52.85   $52.90  
  Purchase #3 $152.71   3.186%   $157.5753   $157.58   $157.60   $157.60  
  Purchase #4 $199.84   7.186%   $214.2005   $214.20   $214.20   $214.20  
  Purchase #5 $62.25   7.561%   $66.9567   $66.96   $66.95   $67.00  
  Purchase #6 $203.74   7.769%   $219.5686   $219.57   $219.55   $219.60  
  Purchase #7 $139.60   8.224%   $151.0807   $151.08   $151.10   $151.10  
  7 purchase totals = $862.37       $924.6271   $924.63   $924.65   $924.80