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 $34.72   7.548%   $37.3407   $37.34   $37.35   $37.30  
  Purchase #2 $168.43   4.324%   $175.7129   $175.71   $175.70   $175.70  
  Purchase #3 $176.68   6.550%   $188.2525   $188.25   $188.25   $188.30  
  Purchase #4 $215.74   4.769%   $226.0286   $226.03   $226.05   $226.00  
  Purchase #5 $88.75   9.108%   $96.8334   $96.83   $96.85   $96.80  
  Purchase #6 $32.55   13.149%   $36.83   $36.83   $36.85   $36.80  
  Purchase #7 $194.30   3.686%   $201.4619   $201.46   $201.45   $201.50  
  7 purchase totals = $911.17       $962.4600   $962.45   $962.50   $962.40