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 $67.37   13.206%   $76.2669   $76.27   $76.25   $76.30  
  Purchase #2 $68.63   4.201%   $71.5131   $71.51   $71.50   $71.50  
  Purchase #3 $240.37   11.694%   $268.4789   $268.48   $268.50   $268.50  
  Purchase #4 $200.25   8.531%   $217.3333   $217.33   $217.35   $217.30  
  Purchase #5 $213.79   10.620%   $236.4945   $236.49   $236.50   $236.50  
  Purchase #6 $119.77   12.107%   $134.2706   $134.27   $134.25   $134.30  
  Purchase #7 $246.28   3.372%   $254.5846   $254.58   $254.60   $254.60  
  7 purchase totals = $1,156.46       $1,258.9419   $1,258.93   $1,258.95   $1,259.00