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 $160.61   8.304%   $173.9471   $173.95   $173.95   $173.90  
  Purchase #2 $219.93   6.103%   $233.3523   $233.35   $233.35   $233.40  
  Purchase #3 $213.43   10.284%   $235.3791   $235.38   $235.40   $235.40  
  Purchase #4 $154.78   5.441%   $163.2016   $163.20   $163.20   $163.20  
  Purchase #5 $125.89   10.213%   $138.7471   $138.75   $138.75   $138.70  
  Purchase #6 $191.99   10.497%   $212.1432   $212.14   $212.15   $212.10  
  Purchase #7 $88.60   11.669%   $98.9387   $98.94   $98.95   $98.90  
  7 purchase totals = $1,155.23       $1,255.7091   $1,255.71   $1,255.75   $1,255.60