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 $119.39   12.316%   $134.0941   $134.09   $134.10   $134.10  
  Purchase #2 $108.94   6.738%   $116.2804   $116.28   $116.30   $116.30  
  Purchase #3 $91.25   5.555%   $96.3189   $96.32   $96.30   $96.30  
  Purchase #4 $211.35   3.727%   $219.227   $219.23   $219.25   $219.20  
  Purchase #5 $217.37   12.568%   $244.6891   $244.69   $244.70   $244.70  
  Purchase #6 $49.41   8.597%   $53.6578   $53.66   $53.65   $53.70  
  Purchase #7 $176.31   4.733%   $184.6548   $184.65   $184.65   $184.70  
  7 purchase totals = $974.02       $1,048.9221   $1,048.92   $1,048.95   $1,049.00