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 $33.65   4.822%   $35.2726   $35.27   $35.25   $35.30  
  Purchase #2 $134.92   7.747%   $145.3723   $145.37   $145.35   $145.40  
  Purchase #3 $113.73   3.265%   $117.4433   $117.44   $117.45   $117.40  
  Purchase #4 $115.32   9.602%   $126.393   $126.39   $126.40   $126.40  
  Purchase #5 $101.43   7.274%   $108.808   $108.81   $108.80   $108.80  
  Purchase #6 $184.94   3.216%   $190.8877   $190.89   $190.90   $190.90  
  Purchase #7 $77.36   3.765%   $80.2726   $80.27   $80.25   $80.30  
  7 purchase totals = $761.35       $804.4495   $804.44   $804.40   $804.50