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 $165.71   9.841%   $182.0175   $182.02   $182.00   $182.00  
  Purchase #2 $138.71   7.399%   $148.9732   $148.97   $148.95   $149.00  
  Purchase #3 $119.42   10.347%   $131.7764   $131.78   $131.80   $131.80  
  Purchase #4 $249.30   7.221%   $267.302   $267.30   $267.30   $267.30  
  Purchase #5 $17.91   12.448%   $20.1394   $20.14   $20.15   $20.10  
  Purchase #6 $50.77   11.161%   $56.4364   $56.44   $56.45   $56.40  
  Purchase #7 $142.61   12.573%   $160.5404   $160.54   $160.55   $160.50  
  7 purchase totals = $884.43       $967.1853   $967.19   $967.20   $967.10