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 $52.47   13.394%   $59.4978   $59.50   $59.50   $59.50  
  Purchase #2 $71.99   6.166%   $76.4289   $76.43   $76.45   $76.40  
  Purchase #3 $172.47   13.400%   $195.581   $195.58   $195.60   $195.60  
  Purchase #4 $122.98   13.824%   $139.9808   $139.98   $140.00   $140.00  
  Purchase #5 $6.58   10.409%   $7.2649   $7.26   $7.25   $7.30  
  Purchase #6 $231.88   6.213%   $246.2867   $246.29   $246.30   $246.30  
  Purchase #7 $6.51   4.609%   $6.81   $6.81   $6.80   $6.80  
  7 purchase totals = $664.88       $731.8501   $731.85   $731.90   $731.90