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 $230.48   13.220%   $260.9495   $260.95   $260.95   $260.90  
  Purchase #2 $141.52   7.672%   $152.3774   $152.38   $152.40   $152.40  
  Purchase #3 $114.77   8.749%   $124.8112   $124.81   $124.80   $124.80  
  Purchase #4 $235.70   11.297%   $262.327   $262.33   $262.35   $262.30  
  Purchase #5 $123.94   11.397%   $138.0654   $138.07   $138.05   $138.10  
  Purchase #6 $77.64   7.355%   $83.3504   $83.35   $83.35   $83.40  
  Purchase #7 $227.63   7.604%   $244.939   $244.94   $244.95   $244.90  
  7 purchase totals = $1,151.68       $1,266.8199   $1,266.83   $1,266.85   $1,266.80