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 $235.56   12.581%   $265.1958   $265.20   $265.20   $265.20  
  Purchase #2 $210.57   8.141%   $227.7125   $227.71   $227.70   $227.70  
  Purchase #3 $209.86   3.164%   $216.5   $216.50   $216.50   $216.50  
  Purchase #4 $120.84   13.197%   $136.7873   $136.79   $136.80   $136.80  
  Purchase #5 $33.95   4.493%   $35.4754   $35.48   $35.50   $35.50  
  Purchase #6 $23.61   3.589%   $24.4574   $24.46   $24.45   $24.50  
  Purchase #7 $119.39   13.452%   $135.4503   $135.45   $135.45   $135.50  
  7 purchase totals = $953.78       $1,041.5787   $1,041.59   $1,041.60   $1,041.70