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 $72.66   13.170%   $82.2293   $82.23   $82.25   $82.20  
  Purchase #2 $205.93   10.817%   $228.2054   $228.21   $228.20   $228.20  
  Purchase #3 $49.48   10.691%   $54.7699   $54.77   $54.75   $54.80  
  Purchase #4 $220.35   8.607%   $239.3155   $239.32   $239.30   $239.30  
  Purchase #5 $44.51   6.475%   $47.392   $47.39   $47.40   $47.40  
  Purchase #6 $238.90   5.296%   $251.5521   $251.55   $251.55   $251.60  
  Purchase #7 $153.81   4.307%   $160.4346   $160.43   $160.45   $160.40  
  7 purchase totals = $985.64       $1,063.8988   $1,063.90   $1,063.90   $1,063.90