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 $54.60   8.757%   $59.3813   $59.38   $59.40   $59.40  
  Purchase #2 $61.95   7.703%   $66.722   $66.72   $66.70   $66.70  
  Purchase #3 $81.94   3.617%   $84.9038   $84.90   $84.90   $84.90  
  Purchase #4 $158.74   7.511%   $170.663   $170.66   $170.65   $170.70  
  Purchase #5 $158.85   7.594%   $170.9131   $170.91   $170.90   $170.90  
  Purchase #6 $68.63   8.818%   $74.6818   $74.68   $74.70   $74.70  
  Purchase #7 $22.27   8.174%   $24.0903   $24.09   $24.10   $24.10  
  7 purchase totals = $606.98       $651.3553   $651.34   $651.35   $651.40