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 $134.99   11.206%   $150.117   $150.12   $150.10   $150.10  
  Purchase #2 $226.97   12.627%   $255.6295   $255.63   $255.65   $255.60  
  Purchase #3 $189.95   8.580%   $206.2477   $206.25   $206.25   $206.20  
  Purchase #4 $210.54   5.800%   $222.7513   $222.75   $222.75   $222.80  
  Purchase #5 $27.91   6.177%   $29.634   $29.63   $29.65   $29.60  
  Purchase #6 $111.80   9.659%   $122.5988   $122.60   $122.60   $122.60  
  Purchase #7 $57.74   10.756%   $63.9505   $63.95   $63.95   $64.00  
  7 purchase totals = $959.90       $1,050.9288   $1,050.93   $1,050.95   $1,050.90