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 $161.97   12.772%   $182.6568   $182.66   $182.65   $182.70  
  Purchase #2 $138.72   4.152%   $144.4797   $144.48   $144.50   $144.50  
  Purchase #3 $170.97   4.862%   $179.2826   $179.28   $179.30   $179.30  
  Purchase #4 $171.84   5.373%   $181.073   $181.07   $181.05   $181.10  
  Purchase #5 $68.54   11.806%   $76.6318   $76.63   $76.65   $76.60  
  Purchase #6 $205.74   7.509%   $221.189   $221.19   $221.20   $221.20  
  Purchase #7 $63.97   6.125%   $67.8882   $67.89   $67.90   $67.90  
  7 purchase totals = $981.75       $1,053.2011   $1,053.20   $1,053.25   $1,053.30