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 $248.68   3.268%   $256.8069   $256.81   $256.80   $256.80  
  Purchase #2 $60.45   7.639%   $65.0678   $65.07   $65.05   $65.10  
  Purchase #3 $212.94   4.666%   $222.8758   $222.88   $222.90   $222.90  
  Purchase #4 $239.55   9.844%   $263.1313   $263.13   $263.15   $263.10  
  Purchase #5 $241.47   7.251%   $258.979   $258.98   $259.00   $259.00  
  Purchase #6 $102.47   5.799%   $108.4122   $108.41   $108.40   $108.40  
  Purchase #7 $56.93   5.680%   $60.1636   $60.16   $60.15   $60.20  
  7 purchase totals = $1,162.49       $1,235.4366   $1,235.44   $1,235.45   $1,235.50