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 $249.29   8.200%   $269.7318   $269.73   $269.75   $269.70  
  Purchase #2 $63.53   8.548%   $68.9605   $68.96   $68.95   $69.00  
  Purchase #3 $94.99   5.270%   $99.996   $100.00   $100.00   $100.00  
  Purchase #4 $47.76   5.199%   $50.243   $50.24   $50.25   $50.20  
  Purchase #5 $190.76   6.236%   $202.6558   $202.66   $202.65   $202.70  
  Purchase #6 $58.61   11.614%   $65.417   $65.42   $65.40   $65.40  
  Purchase #7 $213.95   4.771%   $224.1576   $224.16   $224.15   $224.20  
  7 purchase totals = $918.89       $981.1617   $981.17   $981.15   $981.20