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 $53.77   9.616%   $58.9405   $58.94   $58.95   $58.90  
  Purchase #2 $26.33   7.368%   $28.27   $28.27   $28.25   $28.30  
  Purchase #3 $89.42   4.435%   $93.3858   $93.39   $93.40   $93.40  
  Purchase #4 $15.57   3.404%   $16.1   $16.10   $16.10   $16.10  
  Purchase #5 $57.41   4.700%   $60.1083   $60.11   $60.10   $60.10  
  Purchase #6 $127.70   4.822%   $133.8577   $133.86   $133.85   $133.90  
  Purchase #7 $236.96   13.599%   $269.1842   $269.18   $269.20   $269.20  
  7 purchase totals = $607.16       $659.8465   $659.85   $659.85   $659.90