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	$77.57	7.856%	$83.6639	$83.66	$83.65	$83.70
Purchase #2	$144.86	9.809%	$159.0693	$159.07	$159.05	$159.10
Purchase #3	$64.71	9.873%	$71.0988	$71.10	$71.10	$71.10
Purchase #4	$118.59	11.496%	$132.2231	$132.22	$132.20	$132.20
Purchase #5	$83.78	6.310%	$89.0665	$89.07	$89.05	$89.10
Purchase #6	$139.41	13.379%	$158.0617	$158.06	$158.05	$158.10
Purchase #7	$71.32	7.334%	$76.5506	$76.55	$76.55	$76.60
7 purchase totals =	$700.24		$769.7339	$769.73	$769.65	$769.90