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 $154.26   6.693%   $164.5846   $164.58   $164.60   $164.60  
  Purchase #2 $189.58   4.759%   $198.6021   $198.60   $198.60   $198.60  
  Purchase #3 $42.58   7.742%   $45.8765   $45.88   $45.90   $45.90  
  Purchase #4 $233.28   7.349%   $250.4237   $250.42   $250.40   $250.40  
  Purchase #5 $235.40   13.825%   $267.9441   $267.94   $267.95   $267.90  
  Purchase #6 $99.96   3.670%   $103.6285   $103.63   $103.65   $103.60  
  Purchase #7 $126.79   5.357%   $133.5821   $133.58   $133.60   $133.60  
  7 purchase totals = $1,081.85       $1,164.6416   $1,164.63   $1,164.70   $1,164.60