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 $247.37   8.767%   $269.0569   $269.06   $269.05   $269.10  
  Purchase #2 $107.43   3.235%   $110.9054   $110.91   $110.90   $110.90  
  Purchase #3 $58.53   4.862%   $61.3757   $61.38   $61.40   $61.40  
  Purchase #4 $250.95   11.176%   $278.9962   $279.00   $279.00   $279.00  
  Purchase #5 $137.56   10.712%   $152.2954   $152.30   $152.30   $152.30  
  Purchase #6 $139.74   12.167%   $156.7422   $156.74   $156.75   $156.70  
  Purchase #7 $112.71   12.504%   $126.8033   $126.80   $126.80   $126.80  
  7 purchase totals = $1,054.29       $1,156.1751   $1,156.19   $1,156.20   $1,156.20