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 $192.52   7.523%   $207.0033   $207.00   $207.00   $207.00  
  Purchase #2 $185.26   8.118%   $200.2994   $200.30   $200.30   $200.30  
  Purchase #3 $24.59   9.223%   $26.8579   $26.86   $26.85   $26.90  
  Purchase #4 $51.72   7.523%   $55.6109   $55.61   $55.60   $55.60  
  Purchase #5 $249.42   5.675%   $263.5746   $263.57   $263.55   $263.60  
  Purchase #6 $46.44   11.611%   $51.8321   $51.83   $51.85   $51.80  
  Purchase #7 $236.86   10.450%   $261.6119   $261.61   $261.60   $261.60  
  7 purchase totals = $986.81       $1,066.7901   $1,066.78   $1,066.75   $1,066.80