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 $63.79   12.617%   $71.8384   $71.84   $71.85   $71.80  
  Purchase #2 $195.28   3.393%   $201.9059   $201.91   $201.90   $201.90  
  Purchase #3 $42.48   5.462%   $44.8003   $44.80   $44.80   $44.80  
  Purchase #4 $76.80   9.234%   $83.8917   $83.89   $83.90   $83.90  
  Purchase #5 $180.47   4.699%   $188.9503   $188.95   $188.95   $189.00  
  Purchase #6 $175.83   4.787%   $184.247   $184.25   $184.25   $184.20  
  Purchase #7 $125.41   12.511%   $141.1   $141.10   $141.10   $141.10  
  7 purchase totals = $860.06       $916.7336   $916.74   $916.75   $916.70