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 $55.91   8.227%   $60.5097   $60.51   $60.50   $60.50  
  Purchase #2 $187.58   9.159%   $204.7605   $204.76   $204.75   $204.80  
  Purchase #3 $154.56   4.421%   $161.3931   $161.39   $161.40   $161.40  
  Purchase #4 $28.68   10.495%   $31.69   $31.69   $31.70   $31.70  
  Purchase #5 $168.47   7.106%   $180.4415   $180.44   $180.45   $180.40  
  Purchase #6 $169.55   9.423%   $185.5267   $185.53   $185.55   $185.50  
  Purchase #7 $213.86   7.479%   $229.8546   $229.85   $229.85   $229.90  
  7 purchase totals = $978.61       $1,054.1761   $1,054.17   $1,054.20   $1,054.20