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 $61.41   13.821%   $69.8975   $69.90   $69.90   $69.90  
  Purchase #2 $91.57   10.283%   $100.9861   $100.99   $101.00   $101.00  
  Purchase #3 $6.26   9.858%   $6.8771   $6.88   $6.90   $6.90  
  Purchase #4 $39.27   11.257%   $43.6906   $43.69   $43.70   $43.70  
  Purchase #5 $77.59   4.456%   $81.0474   $81.05   $81.05   $81.00  
  Purchase #6 $33.31   9.540%   $36.4878   $36.49   $36.50   $36.50  
  Purchase #7 $168.84   10.612%   $186.7573   $186.76   $186.75   $186.80  
  7 purchase totals = $478.25       $525.7438   $525.76   $525.80   $525.80