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 $69.82   11.357%   $77.7495   $77.75   $77.75   $77.70  
  Purchase #2 $172.99   5.594%   $182.6671   $182.67   $182.65   $182.70  
  Purchase #3 $106.33   10.173%   $117.147   $117.15   $117.15   $117.10  
  Purchase #4 $24.25   6.750%   $25.8869   $25.89   $25.90   $25.90  
  Purchase #5 $239.26   8.439%   $259.4512   $259.45   $259.45   $259.50  
  Purchase #6 $73.37   5.147%   $77.1464   $77.15   $77.15   $77.10  
  Purchase #7 $12.86   3.542%   $13.3155   $13.32   $13.30   $13.30  
  7 purchase totals = $698.88       $753.3636   $753.38   $753.35   $753.30