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 $202.46   10.788%   $224.3014   $224.30   $224.30   $224.30  
  Purchase #2 $55.41   3.644%   $57.4291   $57.43   $57.45   $57.40  
  Purchase #3 $84.37   12.770%   $95.144   $95.14   $95.15   $95.10  
  Purchase #4 $199.79   7.419%   $214.6124   $214.61   $214.60   $214.60  
  Purchase #5 $115.28   8.477%   $125.0523   $125.05   $125.05   $125.10  
  Purchase #6 $240.59   11.234%   $267.6179   $267.62   $267.60   $267.60  
  Purchase #7 $44.31   6.789%   $47.3182   $47.32   $47.30   $47.30  
  7 purchase totals = $942.21       $1,031.4753   $1,031.47   $1,031.45   $1,031.40