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 $203.68   11.335%   $226.7671   $226.77   $226.75   $226.80  
  Purchase #2 $23.90   3.275%   $24.6827   $24.68   $24.70   $24.70  
  Purchase #3 $93.81   4.765%   $98.28   $98.28   $98.30   $98.30  
  Purchase #4 $101.51   3.874%   $105.4425   $105.44   $105.45   $105.40  
  Purchase #5 $70.52   7.251%   $75.6334   $75.63   $75.65   $75.60  
  Purchase #6 $124.75   12.265%   $140.0506   $140.05   $140.05   $140.10  
  Purchase #7 $163.32   11.501%   $182.1034   $182.10   $182.10   $182.10  
  7 purchase totals = $781.49       $852.9597   $852.95   $853.00   $853.00