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 $52.54   12.393%   $59.0513   $59.05   $59.05   $59.10  
  Purchase #2 $187.38   3.492%   $193.9233   $193.92   $193.90   $193.90  
  Purchase #3 $131.87   5.763%   $139.4697   $139.47   $139.45   $139.50  
  Purchase #4 $149.72   4.837%   $156.962   $156.96   $156.95   $157.00  
  Purchase #5 $195.37   11.698%   $218.2244   $218.22   $218.20   $218.20  
  Purchase #6 $243.69   10.735%   $269.8501   $269.85   $269.85   $269.90  
  Purchase #7 $155.39   7.721%   $167.3877   $167.39   $167.40   $167.40  
  7 purchase totals = $1,115.96       $1,204.8685   $1,204.86   $1,204.80   $1,205.00