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 $62.63   8.641%   $68.0419   $68.04   $68.05   $68.00  
  Purchase #2 $189.69   8.740%   $206.2689   $206.27   $206.25   $206.30  
  Purchase #3 $242.52   3.576%   $251.1925   $251.19   $251.20   $251.20  
  Purchase #4 $63.44   10.602%   $70.1659   $70.17   $70.15   $70.20  
  Purchase #5 $88.33   4.108%   $91.9586   $91.96   $91.95   $92.00  
  Purchase #6 $52.28   7.532%   $56.2177   $56.22   $56.20   $56.20  
  Purchase #7 $37.62   10.389%   $41.5283   $41.53   $41.55   $41.50  
  7 purchase totals = $736.51       $785.3738   $785.38   $785.35   $785.40