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 $141.84   6.658%   $151.2837   $151.28   $151.30   $151.30  
  Purchase #2 $48.38   12.106%   $54.2369   $54.24   $54.25   $54.20  
  Purchase #3 $190.77   6.520%   $203.2082   $203.21   $203.20   $203.20  
  Purchase #4 $56.97   10.701%   $63.0664   $63.07   $63.05   $63.10  
  Purchase #5 $179.69   10.245%   $198.0992   $198.10   $198.10   $198.10  
  Purchase #6 $169.92   10.781%   $188.2391   $188.24   $188.25   $188.20  
  Purchase #7 $69.47   10.570%   $76.813   $76.81   $76.80   $76.80  
  7 purchase totals = $857.04       $934.9465   $934.95   $934.95   $934.90