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 $62.36   3.379%   $64.4671   $64.47   $64.45   $64.50  
  Purchase #2 $132.66   3.726%   $137.6029   $137.60   $137.60   $137.60  
  Purchase #3 $32.84   13.431%   $37.2507   $37.25   $37.25   $37.30  
  Purchase #4 $156.70   12.228%   $175.8613   $175.86   $175.85   $175.90  
  Purchase #5 $105.70   12.534%   $118.9484   $118.95   $118.95   $118.90  
  Purchase #6 $201.36   8.319%   $218.1111   $218.11   $218.10   $218.10  
  Purchase #7 $12.93   7.502%   $13.9   $13.90   $13.90   $13.90  
  7 purchase totals = $704.55       $766.1415   $766.14   $766.10   $766.20