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 $206.57   8.741%   $224.6263   $224.63   $224.65   $224.60  
  Purchase #2 $248.26   10.754%   $274.9579   $274.96   $274.95   $275.00  
  Purchase #3 $37.94   8.205%   $41.053   $41.05   $41.05   $41.10  
  Purchase #4 $30.64   8.130%   $33.131   $33.13   $33.15   $33.10  
  Purchase #5 $201.59   11.248%   $224.2648   $224.26   $224.25   $224.30  
  Purchase #6 $61.65   8.496%   $66.8878   $66.89   $66.90   $66.90  
  Purchase #7 $218.90   10.164%   $241.149   $241.15   $241.15   $241.10  
  7 purchase totals = $1,005.55       $1,106.0698   $1,106.07   $1,106.10   $1,106.10