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 $206.32   8.270%   $223.3827   $223.38   $223.40   $223.40  
  Purchase #2 $210.30   4.827%   $220.4512   $220.45   $220.45   $220.50  
  Purchase #3 $195.81   9.785%   $214.97   $214.97   $214.95   $215.00  
  Purchase #4 $12.42   10.493%   $13.7232   $13.72   $13.70   $13.70  
  Purchase #5 $145.58   10.207%   $160.4394   $160.44   $160.45   $160.40  
  Purchase #6 $158.91   7.149%   $170.2705   $170.27   $170.25   $170.30  
  Purchase #7 $179.46   3.616%   $185.9493   $185.95   $185.95   $185.90  
  7 purchase totals = $1,108.80       $1,189.1863   $1,189.18   $1,189.15   $1,189.20