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 $178.48   13.781%   $203.0763   $203.08   $203.10   $203.10  
  Purchase #2 $43.36   3.111%   $44.7089   $44.71   $44.70   $44.70  
  Purchase #3 $161.25   13.527%   $183.0623   $183.06   $183.05   $183.10  
  Purchase #4 $70.30   8.515%   $76.286   $76.29   $76.30   $76.30  
  Purchase #5 $60.72   6.824%   $64.8635   $64.86   $64.85   $64.90  
  Purchase #6 $159.67   6.277%   $169.6925   $169.69   $169.70   $169.70  
  Purchase #7 $245.40   7.147%   $262.9387   $262.94   $262.95   $262.90  
  7 purchase totals = $919.18       $1,004.6282   $1,004.63   $1,004.65   $1,004.70