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 $46.25   10.683%   $51.1909   $51.19   $51.20   $51.20  
  Purchase #2 $241.43   5.765%   $255.3484   $255.35   $255.35   $255.30  
  Purchase #3 $10.67   9.180%   $11.6495   $11.65   $11.65   $11.60  
  Purchase #4 $194.37   13.433%   $220.4797   $220.48   $220.50   $220.50  
  Purchase #5 $168.63   5.604%   $178.08   $178.08   $178.10   $178.10  
  Purchase #6 $186.89   11.383%   $208.1637   $208.16   $208.15   $208.20  
  Purchase #7 $47.29   4.224%   $49.2875   $49.29   $49.30   $49.30  
  7 purchase totals = $895.53       $974.1997   $974.20   $974.25   $974.20