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 $239.46   9.519%   $262.2542   $262.25   $262.25   $262.30  
  Purchase #2 $38.65   13.732%   $43.9574   $43.96   $43.95   $44.00  
  Purchase #3 $72.46   10.743%   $80.2444   $80.24   $80.25   $80.20  
  Purchase #4 $231.59   6.147%   $245.8258   $245.83   $245.85   $245.80  
  Purchase #5 $125.87   7.214%   $134.9503   $134.95   $134.95   $135.00  
  Purchase #6 $22.44   5.614%   $23.6998   $23.70   $23.70   $23.70  
  Purchase #7 $14.92   7.360%   $16.0181   $16.02   $16.00   $16.00  
  7 purchase totals = $745.39       $806.9500   $806.95   $806.95   $807.00