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 $62.93   13.820%   $71.6269   $71.63   $71.65   $71.60  
  Purchase #2 $24.76   13.838%   $28.1863   $28.19   $28.20   $28.20  
  Purchase #3 $236.91   8.417%   $256.8507   $256.85   $256.85   $256.90  
  Purchase #4 $67.87   11.421%   $75.6214   $75.62   $75.60   $75.60  
  Purchase #5 $210.42   12.603%   $236.9392   $236.94   $236.95   $236.90  
  Purchase #6 $142.73   13.292%   $161.7017   $161.70   $161.70   $161.70  
  Purchase #7 $237.41   13.148%   $268.6247   $268.62   $268.60   $268.60  
  7 purchase totals = $983.03       $1,099.5509   $1,099.55   $1,099.55   $1,099.50