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 $129.49   4.725%   $135.6084   $135.61   $135.60   $135.60  
  Purchase #2 $126.51   13.533%   $143.6306   $143.63   $143.65   $143.60  
  Purchase #3 $122.36   9.403%   $133.8655   $133.87   $133.85   $133.90  
  Purchase #4 $102.76   6.774%   $109.721   $109.72   $109.70   $109.70  
  Purchase #5 $184.56   7.603%   $198.5921   $198.59   $198.60   $198.60  
  Purchase #6 $137.50   5.800%   $145.475   $145.48   $145.50   $145.50  
  Purchase #7 $153.60   7.564%   $165.2183   $165.22   $165.20   $165.20  
  7 purchase totals = $956.78       $1,032.1109   $1,032.12   $1,032.10   $1,032.10