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 $39.97   13.654%   $45.4275   $45.43   $45.45   $45.40  
  Purchase #2 $213.33   12.770%   $240.5722   $240.57   $240.55   $240.60  
  Purchase #3 $50.58   13.687%   $57.5029   $57.50   $57.50   $57.50  
  Purchase #4 $152.66   3.177%   $157.51   $157.51   $157.50   $157.50  
  Purchase #5 $23.32   4.375%   $24.3403   $24.34   $24.35   $24.30  
  Purchase #6 $243.35   13.346%   $275.8275   $275.83   $275.85   $275.80  
  Purchase #7 $77.41   5.221%   $81.4516   $81.45   $81.45   $81.50  
  7 purchase totals = $800.62       $882.6320   $882.63   $882.65   $882.60