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 $60.82   3.142%   $62.731   $62.73   $62.75   $62.70  
  Purchase #2 $179.55   13.265%   $203.3673   $203.37   $203.35   $203.40  
  Purchase #3 $76.83   5.464%   $81.028   $81.03   $81.05   $81.00  
  Purchase #4 $127.96   7.713%   $137.8296   $137.83   $137.85   $137.80  
  Purchase #5 $59.68   5.860%   $63.1772   $63.18   $63.20   $63.20  
  Purchase #6 $229.48   3.382%   $237.241   $237.24   $237.25   $237.20  
  Purchase #7 $54.65   10.102%   $60.1707   $60.17   $60.15   $60.20  
  7 purchase totals = $788.97       $845.5448   $845.55   $845.60   $845.50