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 $93.27   5.783%   $98.6638   $98.66   $98.65   $98.70  
  Purchase #2 $62.95   12.662%   $70.9207   $70.92   $70.90   $70.90  
  Purchase #3 $246.54   10.201%   $271.6895   $271.69   $271.70   $271.70  
  Purchase #4 $247.44   8.275%   $267.9157   $267.92   $267.90   $267.90  
  Purchase #5 $120.47   13.643%   $136.9057   $136.91   $136.90   $136.90  
  Purchase #6 $146.67   5.615%   $154.9055   $154.91   $154.90   $154.90  
  Purchase #7 $30.54   6.238%   $32.4451   $32.45   $32.45   $32.40  
  7 purchase totals = $947.88       $1,033.4460   $1,033.46   $1,033.40   $1,033.40