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 $246.62   3.661%   $255.6488   $255.65   $255.65   $255.60  
  Purchase #2 $184.63   9.331%   $201.8578   $201.86   $201.85   $201.90  
  Purchase #3 $250.46   5.701%   $264.7387   $264.74   $264.75   $264.70  
  Purchase #4 $242.81   13.839%   $276.4125   $276.41   $276.40   $276.40  
  Purchase #5 $60.96   9.337%   $66.6518   $66.65   $66.65   $66.70  
  Purchase #6 $92.44   4.404%   $96.5111   $96.51   $96.50   $96.50  
  Purchase #7 $89.25   8.203%   $96.5712   $96.57   $96.55   $96.60  
  7 purchase totals = $1,167.17       $1,258.3919   $1,258.39   $1,258.35   $1,258.40