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 $183.48   4.180%   $191.1495   $191.15   $191.15   $191.10  
  Purchase #2 $58.98   11.275%   $65.63   $65.63   $65.65   $65.60  
  Purchase #3 $219.33   13.217%   $248.3188   $248.32   $248.30   $248.30  
  Purchase #4 $110.81   6.183%   $117.6614   $117.66   $117.65   $117.70  
  Purchase #5 $230.27   10.110%   $253.5503   $253.55   $253.55   $253.60  
  Purchase #6 $47.68   10.583%   $52.726   $52.73   $52.75   $52.70  
  Purchase #7 $210.40   9.729%   $230.8698   $230.87   $230.85   $230.90  
  7 purchase totals = $1,060.95       $1,159.9058   $1,159.91   $1,159.90   $1,159.90