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 $24.34   4.372%   $25.4041   $25.40   $25.40   $25.40  
  Purchase #2 $190.38   3.796%   $197.6068   $197.61   $197.60   $197.60  
  Purchase #3 $143.95   8.711%   $156.4895   $156.49   $156.50   $156.50  
  Purchase #4 $163.31   12.349%   $183.4772   $183.48   $183.50   $183.50  
  Purchase #5 $131.38   13.504%   $149.1216   $149.12   $149.10   $149.10  
  Purchase #6 $216.76   6.102%   $229.9867   $229.99   $230.00   $230.00  
  Purchase #7 $110.99   13.141%   $125.5752   $125.58   $125.60   $125.60  
  7 purchase totals = $981.11       $1,067.6611   $1,067.67   $1,067.70   $1,067.70