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 $228.86   11.436%   $255.0324   $255.03   $255.05   $255.00  
  Purchase #2 $17.73   10.591%   $19.6078   $19.61   $19.60   $19.60  
  Purchase #3 $164.40   8.633%   $178.5927   $178.59   $178.60   $178.60  
  Purchase #4 $11.25   6.169%   $11.944   $11.94   $11.95   $11.90  
  Purchase #5 $208.64   4.255%   $217.5176   $217.52   $217.50   $217.50  
  Purchase #6 $153.89   9.805%   $168.9789   $168.98   $169.00   $169.00  
  Purchase #7 $188.84   9.409%   $206.608   $206.61   $206.60   $206.60  
  7 purchase totals = $973.61       $1,058.2814   $1,058.28   $1,058.30   $1,058.20