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 $53.85   10.784%   $59.6572   $59.66   $59.65   $59.70  
  Purchase #2 $226.36   4.356%   $236.2202   $236.22   $236.20   $236.20  
  Purchase #3 $14.92   13.367%   $16.9144   $16.91   $16.90   $16.90  
  Purchase #4 $223.69   8.324%   $242.31   $242.31   $242.30   $242.30  
  Purchase #5 $236.83   3.421%   $244.932   $244.93   $244.95   $244.90  
  Purchase #6 $19.30   4.622%   $20.192   $20.19   $20.20   $20.20  
  Purchase #7 $196.61   5.294%   $207.0185   $207.02   $207.00   $207.00  
  7 purchase totals = $971.56       $1,027.2443   $1,027.24   $1,027.20   $1,027.20