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 $244.73   4.482%   $255.6988   $255.70   $255.70   $255.70  
  Purchase #2 $215.82   7.405%   $231.8015   $231.80   $231.80   $231.80  
  Purchase #3 $140.27   7.321%   $150.5392   $150.54   $150.55   $150.50  
  Purchase #4 $86.79   11.707%   $96.9505   $96.95   $96.95   $97.00  
  Purchase #5 $197.91   13.639%   $224.9029   $224.90   $224.90   $224.90  
  Purchase #6 $211.27   10.711%   $233.8991   $233.90   $233.90   $233.90  
  Purchase #7 $106.92   9.741%   $117.3351   $117.34   $117.35   $117.30  
  7 purchase totals = $1,203.71       $1,311.1271   $1,311.13   $1,311.15   $1,311.10