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 $84.49   10.453%   $93.3217   $93.32   $93.30   $93.30  
  Purchase #2 $41.67   6.640%   $44.4369   $44.44   $44.45   $44.40  
  Purchase #3 $197.77   5.306%   $208.2637   $208.26   $208.25   $208.30  
  Purchase #4 $7.55   7.612%   $8.1247   $8.12   $8.10   $8.10  
  Purchase #5 $71.79   6.374%   $76.3659   $76.37   $76.35   $76.40  
  Purchase #6 $202.85   10.691%   $224.5367   $224.54   $224.55   $224.50  
  Purchase #7 $113.51   3.481%   $117.4613   $117.46   $117.45   $117.50  
  7 purchase totals = $719.63       $772.5109   $772.51   $772.45   $772.50