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 $81.94   5.836%   $86.722   $86.72   $86.70   $86.70  
  Purchase #2 $233.63   11.530%   $260.5675   $260.57   $260.55   $260.60  
  Purchase #3 $218.97   7.732%   $235.9008   $235.90   $235.90   $235.90  
  Purchase #4 $208.46   11.254%   $231.9201   $231.92   $231.90   $231.90  
  Purchase #5 $250.65   6.676%   $267.3834   $267.38   $267.40   $267.40  
  Purchase #6 $29.99   6.542%   $31.9519   $31.95   $31.95   $32.00  
  Purchase #7 $93.64   5.783%   $99.0552   $99.06   $99.05   $99.10  
  7 purchase totals = $1,117.28       $1,213.5009   $1,213.50   $1,213.45   $1,213.60