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 $77.33   9.598%   $84.7521   $84.75   $84.75   $84.80  
  Purchase #2 $77.53   11.659%   $86.5692   $86.57   $86.55   $86.60  
  Purchase #3 $131.97   10.626%   $145.9931   $145.99   $146.00   $146.00  
  Purchase #4 $28.78   8.847%   $31.3262   $31.33   $31.35   $31.30  
  Purchase #5 $232.70   4.821%   $243.9185   $243.92   $243.90   $243.90  
  Purchase #6 $113.76   4.606%   $118.9998   $119.00   $119.00   $119.00  
  Purchase #7 $49.30   5.218%   $51.8725   $51.87   $51.85   $51.90  
  7 purchase totals = $711.37       $763.4314   $763.43   $763.40   $763.50