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 $60.65   4.661%   $63.4769   $63.48   $63.50   $63.50  
  Purchase #2 $230.38   12.861%   $260.0092   $260.01   $260.00   $260.00  
  Purchase #3 $154.91   13.237%   $175.4154   $175.42   $175.40   $175.40  
  Purchase #4 $169.92   9.869%   $186.6894   $186.69   $186.70   $186.70  
  Purchase #5 $105.78   8.562%   $114.8369   $114.84   $114.85   $114.80  
  Purchase #6 $136.98   13.583%   $155.586   $155.59   $155.60   $155.60  
  Purchase #7 $45.40   7.769%   $48.9271   $48.93   $48.95   $48.90  
  7 purchase totals = $904.02       $1,004.9409   $1,004.96   $1,005.00   $1,004.90