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	$216.48	12.284%	$243.0724	$243.07	$243.05	$243.10
Purchase #2	$221.96	13.115%	$251.0701	$251.07	$251.05	$251.10
Purchase #3	$140.33	9.856%	$154.1609	$154.16	$154.15	$154.20
Purchase #4	$38.83	8.323%	$42.0618	$42.06	$42.05	$42.10
Purchase #5	$132.39	3.571%	$137.1176	$137.12	$137.10	$137.10
Purchase #6	$51.41	8.478%	$55.7685	$55.77	$55.75	$55.80
Purchase #7	$81.73	9.287%	$89.3203	$89.32	$89.30	$89.30
7 purchase totals =	$883.13		$972.5716	$972.57	$972.45	$972.70