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 $49.49   5.116%   $52.0219   $52.02   $52.00   $52.00  
  Purchase #2 $182.77   10.704%   $202.3337   $202.33   $202.35   $202.30  
  Purchase #3 $50.68   9.507%   $55.4981   $55.50   $55.50   $55.50  
  Purchase #4 $149.77   7.711%   $161.3188   $161.32   $161.30   $161.30  
  Purchase #5 $248.67   6.803%   $265.587   $265.59   $265.60   $265.60  
  Purchase #6 $113.84   3.310%   $117.6081   $117.61   $117.60   $117.60  
  Purchase #7 $178.29   4.494%   $186.3024   $186.30   $186.30   $186.30  
  7 purchase totals = $973.51       $1,040.6700   $1,040.67   $1,040.65   $1,040.60