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 $213.37   13.224%   $241.586   $241.59   $241.60   $241.60  
  Purchase #2 $32.55   12.610%   $36.6546   $36.65   $36.65   $36.70  
  Purchase #3 $102.91   13.861%   $117.1744   $117.17   $117.15   $117.20  
  Purchase #4 $177.47   12.195%   $199.1125   $199.11   $199.10   $199.10  
  Purchase #5 $135.36   13.731%   $153.9463   $153.95   $153.95   $153.90  
  Purchase #6 $175.87   7.184%   $188.5045   $188.50   $188.50   $188.50  
  Purchase #7 $181.78   13.508%   $206.3348   $206.33   $206.35   $206.30  
  7 purchase totals = $1,019.31       $1,143.3131   $1,143.30   $1,143.30   $1,143.30