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 $46.97   7.727%   $50.5994   $50.60   $50.60   $50.60  
  Purchase #2 $6.91   8.530%   $7.4994   $7.50   $7.50   $7.50  
  Purchase #3 $129.65   3.189%   $133.7845   $133.78   $133.80   $133.80  
  Purchase #4 $93.73   4.769%   $98.2   $98.20   $98.20   $98.20  
  Purchase #5 $193.46   5.795%   $204.671   $204.67   $204.65   $204.70  
  Purchase #6 $143.27   3.367%   $148.0939   $148.09   $148.10   $148.10  
  Purchase #7 $113.39   4.722%   $118.7443   $118.74   $118.75   $118.70  
  7 purchase totals = $727.38       $761.5925   $761.58   $761.60   $761.60