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 $105.59   13.265%   $119.5965   $119.60   $119.60   $119.60  
  Purchase #2 $9.86   7.237%   $10.5736   $10.57   $10.55   $10.60  
  Purchase #3 $110.40   7.135%   $118.277   $118.28   $118.30   $118.30  
  Purchase #4 $203.40   11.156%   $226.0913   $226.09   $226.10   $226.10  
  Purchase #5 $23.54   7.407%   $25.2836   $25.28   $25.30   $25.30  
  Purchase #6 $168.88   3.437%   $174.6844   $174.68   $174.70   $174.70  
  Purchase #7 $176.72   3.116%   $182.2266   $182.23   $182.25   $182.20  
  7 purchase totals = $798.39       $856.7330   $856.73   $856.80   $856.80