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 $8.99   12.685%   $10.1304   $10.13   $10.15   $10.10  
  Purchase #2 $103.56   4.354%   $108.069   $108.07   $108.05   $108.10  
  Purchase #3 $248.58   3.601%   $257.5314   $257.53   $257.55   $257.50  
  Purchase #4 $158.47   6.253%   $168.3791   $168.38   $168.40   $168.40  
  Purchase #5 $11.76   6.139%   $12.4819   $12.48   $12.50   $12.50  
  Purchase #6 $183.45   8.768%   $199.5349   $199.53   $199.55   $199.50  
  Purchase #7 $132.93   4.172%   $138.4758   $138.48   $138.50   $138.50  
  7 purchase totals = $847.74       $894.6025   $894.60   $894.70   $894.60