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 $64.94   5.415%   $68.4565   $68.46   $68.45   $68.50  
  Purchase #2 $193.33   8.476%   $209.7167   $209.72   $209.70   $209.70  
  Purchase #3 $215.93   5.337%   $227.4542   $227.45   $227.45   $227.50  
  Purchase #4 $236.88   3.231%   $244.5336   $244.53   $244.55   $244.50  
  Purchase #5 $98.83   3.802%   $102.5875   $102.59   $102.60   $102.60  
  Purchase #6 $182.60   7.264%   $195.8641   $195.86   $195.85   $195.90  
  Purchase #7 $27.53   12.120%   $30.8666   $30.87   $30.85   $30.90  
  7 purchase totals = $1,020.04       $1,079.4792   $1,079.48   $1,079.45   $1,079.60