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 $176.33   10.138%   $194.2063   $194.21   $194.20   $194.20  
  Purchase #2 $63.58   3.241%   $65.6406   $65.64   $65.65   $65.60  
  Purchase #3 $233.26   7.332%   $250.3626   $250.36   $250.35   $250.40  
  Purchase #4 $85.34   13.191%   $96.5972   $96.60   $96.60   $96.60  
  Purchase #5 $212.46   3.716%   $220.355   $220.36   $220.35   $220.40  
  Purchase #6 $206.75   12.384%   $232.3539   $232.35   $232.35   $232.40  
  Purchase #7 $138.32   5.597%   $146.0618   $146.06   $146.05   $146.10  
  7 purchase totals = $1,116.04       $1,205.5774   $1,205.58   $1,205.55   $1,205.70