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 $147.61   13.148%   $167.0178   $167.02   $167.00   $167.00  
  Purchase #2 $35.63   7.106%   $38.1619   $38.16   $38.15   $38.20  
  Purchase #3 $159.71   3.725%   $165.6592   $165.66   $165.65   $165.70  
  Purchase #4 $110.53   12.590%   $124.4457   $124.45   $124.45   $124.40  
  Purchase #5 $71.61   7.828%   $77.2156   $77.22   $77.20   $77.20  
  Purchase #6 $223.87   8.665%   $243.2683   $243.27   $243.25   $243.30  
  Purchase #7 $70.72   7.756%   $76.205   $76.21   $76.20   $76.20  
  7 purchase totals = $819.68       $891.9735   $891.99   $891.90   $892.00