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 $234.95   3.197%   $242.4614   $242.46   $242.45   $242.50  
  Purchase #2 $233.33   5.834%   $246.9425   $246.94   $246.95   $246.90  
  Purchase #3 $20.88   12.708%   $23.5334   $23.53   $23.55   $23.50  
  Purchase #4 $184.31   9.436%   $201.7015   $201.70   $201.70   $201.70  
  Purchase #5 $238.29   12.474%   $268.0143   $268.01   $268.00   $268.00  
  Purchase #6 $89.99   6.680%   $96.0013   $96.00   $96.00   $96.00  
  Purchase #7 $73.75   11.106%   $81.9407   $81.94   $81.95   $81.90  
  7 purchase totals = $1,075.50       $1,160.5951   $1,160.58   $1,160.60   $1,160.50