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 $61.78   10.247%   $68.1106   $68.11   $68.10   $68.10  
  Purchase #2 $152.29   5.656%   $160.9035   $160.90   $160.90   $160.90  
  Purchase #3 $73.26   11.198%   $81.4637   $81.46   $81.45   $81.50  
  Purchase #4 $29.93   12.643%   $33.714   $33.71   $33.70   $33.70  
  Purchase #5 $162.87   9.697%   $178.6635   $178.66   $178.65   $178.70  
  Purchase #6 $235.42   10.523%   $260.1932   $260.19   $260.20   $260.20  
  Purchase #7 $168.40   9.489%   $184.3795   $184.38   $184.40   $184.40  
  7 purchase totals = $883.95       $967.4280   $967.41   $967.40   $967.50