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 $166.69   11.510%   $185.876   $185.88   $185.90   $185.90  
  Purchase #2 $43.66   7.399%   $46.8904   $46.89   $46.90   $46.90  
  Purchase #3 $226.42   8.204%   $244.9955   $245.00   $245.00   $245.00  
  Purchase #4 $55.41   11.323%   $61.6841   $61.68   $61.70   $61.70  
  Purchase #5 $101.72   3.127%   $104.9008   $104.90   $104.90   $104.90  
  Purchase #6 $209.74   4.407%   $218.9832   $218.98   $219.00   $219.00  
  Purchase #7 $65.72   12.115%   $73.682   $73.68   $73.70   $73.70  
  7 purchase totals = $869.36       $937.0120   $937.01   $937.10   $937.10