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	$243.90	12.315%	$273.9363	$273.94	$273.95	$273.90
Purchase #2	$209.74	3.385%	$216.8397	$216.84	$216.85	$216.80
Purchase #3	$171.27	8.635%	$186.0592	$186.06	$186.05	$186.10
Purchase #4	$150.27	9.674%	$164.8071	$164.81	$164.80	$164.80
Purchase #5	$22.93	11.250%	$25.5096	$25.51	$25.50	$25.50
Purchase #6	$163.75	5.192%	$172.2519	$172.25	$172.25	$172.30
Purchase #7	$64.67	12.824%	$72.9633	$72.96	$72.95	$73.00
7 purchase totals =	$1,026.53		$1,112.3671	$1,112.37	$1,112.35	$1,112.40