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 $146.72   4.489%   $153.3063   $153.31   $153.30   $153.30  
  Purchase #2 $249.99   8.784%   $271.9491   $271.95   $271.95   $271.90  
  Purchase #3 $21.89   13.285%   $24.7981   $24.80   $24.80   $24.80  
  Purchase #4 $82.91   10.606%   $91.7034   $91.70   $91.70   $91.70  
  Purchase #5 $218.58   6.522%   $232.8358   $232.84   $232.85   $232.80  
  Purchase #6 $205.66   4.430%   $214.7707   $214.77   $214.75   $214.80  
  Purchase #7 $41.82   13.401%   $47.4243   $47.42   $47.40   $47.40  
  7 purchase totals = $967.57       $1,036.7877   $1,036.79   $1,036.75   $1,036.70