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 $243.66   7.469%   $261.859   $261.86   $261.85   $261.90  
  Purchase #2 $22.99   11.465%   $25.6258   $25.63   $25.65   $25.60  
  Purchase #3 $237.49   7.145%   $254.4587   $254.46   $254.45   $254.50  
  Purchase #4 $125.91   10.815%   $139.5272   $139.53   $139.55   $139.50  
  Purchase #5 $146.57   11.693%   $163.7084   $163.71   $163.70   $163.70  
  Purchase #6 $181.68   6.519%   $193.5237   $193.52   $193.50   $193.50  
  Purchase #7 $137.41   7.868%   $148.2214   $148.22   $148.20   $148.20  
  7 purchase totals = $1,095.71       $1,186.9242   $1,186.93   $1,186.90   $1,186.90