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	$18.68	10.502%	$20.6418	$20.64	$20.65	$20.60
Purchase #2	$159.57	12.595%	$179.6678	$179.67	$179.65	$179.70
Purchase #3	$175.78	12.497%	$197.7472	$197.75	$197.75	$197.70
Purchase #4	$226.48	5.259%	$238.3906	$238.39	$238.40	$238.40
Purchase #5	$80.36	9.829%	$88.2586	$88.26	$88.25	$88.30
Purchase #6	$57.88	3.481%	$59.8948	$59.89	$59.90	$59.90
Purchase #7	$229.51	11.285%	$255.4102	$255.41	$255.40	$255.40
7 purchase totals =	$948.26		$1,040.0110	$1,040.01	$1,040.00	$1,040.00