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 $237.85   13.487%   $269.9288   $269.93   $269.95   $269.90  
  Purchase #2 $146.87   3.194%   $151.561   $151.56   $151.55   $151.60  
  Purchase #3 $76.88   9.465%   $84.1567   $84.16   $84.15   $84.20  
  Purchase #4 $5.94   8.510%   $6.4455   $6.45   $6.45   $6.40  
  Purchase #5 $54.87   7.228%   $58.836   $58.84   $58.85   $58.80  
  Purchase #6 $155.34   5.298%   $163.5699   $163.57   $163.55   $163.60  
  Purchase #7 $24.30   8.307%   $26.3186   $26.32   $26.30   $26.30  
  7 purchase totals = $702.05       $760.8165   $760.83   $760.80   $760.80