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 $11.26   8.763%   $12.2467   $12.25   $12.25   $12.20  
  Purchase #2 $162.29   10.232%   $178.8955   $178.90   $178.90   $178.90  
  Purchase #3 $204.25   9.656%   $223.9724   $223.97   $223.95   $224.00  
  Purchase #4 $248.42   8.392%   $269.2674   $269.27   $269.25   $269.30  
  Purchase #5 $133.75   12.195%   $150.0608   $150.06   $150.05   $150.10  
  Purchase #6 $11.61   9.236%   $12.6823   $12.68   $12.70   $12.70  
  Purchase #7 $56.44   11.591%   $62.982   $62.98   $63.00   $63.00  
  7 purchase totals = $828.02       $910.1071   $910.11   $910.10   $910.20