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 $58.53   4.112%   $60.9368   $60.94   $60.95   $60.90  
  Purchase #2 $35.43   12.121%   $39.7245   $39.72   $39.70   $39.70  
  Purchase #3 $111.61   13.563%   $126.7477   $126.75   $126.75   $126.70  
  Purchase #4 $70.34   4.759%   $73.6875   $73.69   $73.70   $73.70  
  Purchase #5 $142.49   7.171%   $152.708   $152.71   $152.70   $152.70  
  Purchase #6 $216.63   8.542%   $235.1345   $235.13   $235.15   $235.10  
  Purchase #7 $21.83   3.268%   $22.5434   $22.54   $22.55   $22.50  
  7 purchase totals = $656.86       $711.4824   $711.48   $711.50   $711.30