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 $39.52   12.194%   $44.3391   $44.34   $44.35   $44.30  
  Purchase #2 $201.87   6.740%   $215.476   $215.48   $215.50   $215.50  
  Purchase #3 $62.63   8.669%   $68.0594   $68.06   $68.05   $68.10  
  Purchase #4 $182.84   13.784%   $208.0427   $208.04   $208.05   $208.00  
  Purchase #5 $207.58   7.373%   $222.8849   $222.88   $222.90   $222.90  
  Purchase #6 $34.97   11.798%   $39.0958   $39.10   $39.10   $39.10  
  Purchase #7 $45.99   11.234%   $51.1565   $51.16   $51.15   $51.20  
  7 purchase totals = $775.40       $849.0544   $849.06   $849.10   $849.10