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 $246.79   4.362%   $257.555   $257.56   $257.55   $257.60  
  Purchase #2 $56.73   9.116%   $61.9015   $61.90   $61.90   $61.90  
  Purchase #3 $114.36   9.272%   $124.9635   $124.96   $124.95   $125.00  
  Purchase #4 $203.54   6.526%   $216.823   $216.82   $216.80   $216.80  
  Purchase #5 $175.45   10.274%   $193.4757   $193.48   $193.50   $193.50  
  Purchase #6 $205.92   10.282%   $227.0927   $227.09   $227.10   $227.10  
  Purchase #7 $67.89   7.246%   $72.8093   $72.81   $72.80   $72.80  
  7 purchase totals = $1,070.68       $1,154.6207   $1,154.62   $1,154.60   $1,154.70