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 $91.86   13.762%   $104.5018   $104.50   $104.50   $104.50  
  Purchase #2 $21.30   13.626%   $24.2023   $24.20   $24.20   $24.20  
  Purchase #3 $87.51   10.419%   $96.6277   $96.63   $96.65   $96.60  
  Purchase #4 $60.50   3.598%   $62.6768   $62.68   $62.70   $62.70  
  Purchase #5 $229.47   5.854%   $242.9032   $242.90   $242.90   $242.90  
  Purchase #6 $192.55   9.269%   $210.3975   $210.40   $210.40   $210.40  
  Purchase #7 $92.27   4.269%   $96.209   $96.21   $96.20   $96.20  
  7 purchase totals = $775.46       $837.5183   $837.52   $837.55   $837.50