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 $146.82   7.322%   $157.5702   $157.57   $157.55   $157.60  
  Purchase #2 $39.75   3.843%   $41.2776   $41.28   $41.30   $41.30  
  Purchase #3 $78.92   8.814%   $85.876   $85.88   $85.90   $85.90  
  Purchase #4 $36.87   11.284%   $41.0304   $41.03   $41.05   $41.00  
  Purchase #5 $200.27   4.694%   $209.6707   $209.67   $209.65   $209.70  
  Purchase #6 $86.48   13.602%   $98.243   $98.24   $98.25   $98.20  
  Purchase #7 $69.65   11.478%   $77.6444   $77.64   $77.65   $77.60  
  7 purchase totals = $658.76       $711.3123   $711.31   $711.35   $711.30