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 $242.77   13.771%   $276.2019   $276.20   $276.20   $276.20  
  Purchase #2 $210.73   9.274%   $230.2731   $230.27   $230.25   $230.30  
  Purchase #3 $23.93   6.555%   $25.4986   $25.50   $25.50   $25.50  
  Purchase #4 $246.85   11.258%   $274.6404   $274.64   $274.65   $274.60  
  Purchase #5 $183.64   3.232%   $189.5752   $189.58   $189.60   $189.60  
  Purchase #6 $219.82   11.494%   $245.0861   $245.09   $245.10   $245.10  
  Purchase #7 $27.85   6.350%   $29.6185   $29.62   $29.60   $29.60  
  7 purchase totals = $1,155.59       $1,270.8938   $1,270.90   $1,270.90   $1,270.90