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 $153.26   11.631%   $171.0857   $171.09   $171.10   $171.10  
  Purchase #2 $136.51   11.331%   $151.9779   $151.98   $152.00   $152.00  
  Purchase #3 $194.61   10.676%   $215.3866   $215.39   $215.40   $215.40  
  Purchase #4 $160.25   9.824%   $175.993   $175.99   $176.00   $176.00  
  Purchase #5 $159.91   10.420%   $176.5726   $176.57   $176.55   $176.60  
  Purchase #6 $233.77   13.181%   $264.5832   $264.58   $264.60   $264.60  
  Purchase #7 $46.42   5.158%   $48.8143   $48.81   $48.80   $48.80  
  7 purchase totals = $1,084.73       $1,204.4133   $1,204.41   $1,204.45   $1,204.50