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 $184.62   11.581%   $206.0008   $206.00   $206.00   $206.00  
  Purchase #2 $64.78   10.624%   $71.6622   $71.66   $71.65   $71.70  
  Purchase #3 $173.97   11.604%   $194.1575   $194.16   $194.15   $194.20  
  Purchase #4 $75.67   7.409%   $81.2764   $81.28   $81.30   $81.30  
  Purchase #5 $55.71   13.562%   $63.2654   $63.27   $63.25   $63.30  
  Purchase #6 $122.83   7.817%   $132.4316   $132.43   $132.45   $132.40  
  Purchase #7 $14.42   11.111%   $16.0222   $16.02   $16.00   $16.00  
  7 purchase totals = $692.00       $764.8161   $764.82   $764.80   $764.90