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 $238.61   12.111%   $267.5081   $267.51   $267.50   $267.50  
  Purchase #2 $23.49   4.314%   $24.5034   $24.50   $24.50   $24.50  
  Purchase #3 $108.28   8.654%   $117.6506   $117.65   $117.65   $117.70  
  Purchase #4 $135.68   8.511%   $147.2277   $147.23   $147.25   $147.20  
  Purchase #5 $33.62   6.292%   $35.7354   $35.74   $35.75   $35.70  
  Purchase #6 $11.43   5.480%   $12.0564   $12.06   $12.05   $12.10  
  Purchase #7 $250.60   7.311%   $268.9214   $268.92   $268.90   $268.90  
  7 purchase totals = $801.71       $873.6030   $873.61   $873.60   $873.60