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 $245.71   8.642%   $266.9443   $266.94   $266.95   $266.90  
  Purchase #2 $30.62   8.654%   $33.2699   $33.27   $33.25   $33.30  
  Purchase #3 $246.82   11.338%   $274.8045   $274.80   $274.80   $274.80  
  Purchase #4 $106.94   4.336%   $111.5769   $111.58   $111.60   $111.60  
  Purchase #5 $212.94   4.396%   $222.3008   $222.30   $222.30   $222.30  
  Purchase #6 $22.47   5.761%   $23.7645   $23.76   $23.75   $23.80  
  Purchase #7 $87.42   6.722%   $93.2964   $93.30   $93.30   $93.30  
  7 purchase totals = $952.92       $1,025.9573   $1,025.95   $1,025.95   $1,026.00