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	$57.60	3.425%	$59.5728	$59.57	$59.55	$59.60
Purchase #2	$109.66	4.705%	$114.8195	$114.82	$114.80	$114.80
Purchase #3	$80.48	11.511%	$89.7441	$89.74	$89.75	$89.70
Purchase #4	$74.84	11.829%	$83.6928	$83.69	$83.70	$83.70
Purchase #5	$221.61	7.820%	$238.9399	$238.94	$238.95	$238.90
Purchase #6	$70.91	8.444%	$76.8976	$76.90	$76.90	$76.90
Purchase #7	$130.59	12.608%	$147.0548	$147.05	$147.05	$147.10
7 purchase totals =	$745.69		$810.7215	$810.71	$810.70	$810.70