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 $35.35   6.189%   $37.5378   $37.54   $37.55   $37.50  
  Purchase #2 $211.79   6.326%   $225.1878   $225.19   $225.20   $225.20  
  Purchase #3 $244.69   3.285%   $252.7281   $252.73   $252.75   $252.70  
  Purchase #4 $59.42   6.559%   $63.3174   $63.32   $63.30   $63.30  
  Purchase #5 $102.79   10.844%   $113.9365   $113.94   $113.95   $113.90  
  Purchase #6 $248.99   9.365%   $272.3079   $272.31   $272.30   $272.30  
  Purchase #7 $153.95   9.209%   $168.1273   $168.13   $168.15   $168.10  
  7 purchase totals = $1,056.98       $1,133.1428   $1,133.16   $1,133.20   $1,133.00