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 $65.79   13.548%   $74.7032   $74.70   $74.70   $74.70  
  Purchase #2 $111.45   5.313%   $117.3713   $117.37   $117.35   $117.40  
  Purchase #3 $151.38   10.678%   $167.5444   $167.54   $167.55   $167.50  
  Purchase #4 $117.64   3.391%   $121.6292   $121.63   $121.65   $121.60  
  Purchase #5 $162.64   6.736%   $173.5954   $173.60   $173.60   $173.60  
  Purchase #6 $177.36   6.288%   $188.5124   $188.51   $188.50   $188.50  
  Purchase #7 $194.94   13.579%   $221.4109   $221.41   $221.40   $221.40  
  7 purchase totals = $981.20       $1,064.7668   $1,064.76   $1,064.75   $1,064.70