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 $152.58   8.504%   $165.5554   $165.56   $165.55   $165.60  
  Purchase #2 $84.56   11.692%   $94.4468   $94.45   $94.45   $94.40  
  Purchase #3 $216.71   12.828%   $244.5096   $244.51   $244.50   $244.50  
  Purchase #4 $190.48   3.359%   $196.8782   $196.88   $196.90   $196.90  
  Purchase #5 $210.47   3.873%   $218.6215   $218.62   $218.60   $218.60  
  Purchase #6 $193.28   7.835%   $208.4235   $208.42   $208.40   $208.40  
  Purchase #7 $77.50   9.222%   $84.6471   $84.65   $84.65   $84.60  
  7 purchase totals = $1,125.58       $1,213.0821   $1,213.09   $1,213.05   $1,213.00