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 $30.36   7.143%   $32.5286   $32.53   $32.55   $32.50  
  Purchase #2 $187.52   7.321%   $201.2483   $201.25   $201.25   $201.20  
  Purchase #3 $160.51   6.588%   $171.0844   $171.08   $171.10   $171.10  
  Purchase #4 $14.96   6.654%   $15.9554   $15.96   $15.95   $16.00  
  Purchase #5 $48.33   4.766%   $50.6334   $50.63   $50.65   $50.60  
  Purchase #6 $224.66   11.412%   $250.2982   $250.30   $250.30   $250.30  
  Purchase #7 $84.72   13.657%   $96.2902   $96.29   $96.30   $96.30  
  7 purchase totals = $751.06       $818.0385   $818.04   $818.10   $818.00