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 $65.93   5.544%   $69.5852   $69.59   $69.60   $69.60  
  Purchase #2 $17.63   11.809%   $19.7119   $19.71   $19.70   $19.70  
  Purchase #3 $223.89   8.533%   $242.9945   $242.99   $243.00   $243.00  
  Purchase #4 $184.53   4.150%   $192.188   $192.19   $192.20   $192.20  
  Purchase #5 $51.82   10.824%   $57.429   $57.43   $57.45   $57.40  
  Purchase #6 $194.39   5.344%   $204.7782   $204.78   $204.80   $204.80  
  Purchase #7 $223.86   5.619%   $236.4387   $236.44   $236.45   $236.40  
  7 purchase totals = $962.05       $1,023.1255   $1,023.13   $1,023.20   $1,023.10