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	$31.62	6.867%	$33.7913	$33.79	$33.80	$33.80
Purchase #2	$129.89	7.271%	$139.3343	$139.33	$139.35	$139.30
Purchase #3	$235.59	6.410%	$250.6913	$250.69	$250.70	$250.70
Purchase #4	$106.32	7.624%	$114.4258	$114.43	$114.45	$114.40
Purchase #5	$191.30	12.419%	$215.0575	$215.06	$215.05	$215.10
Purchase #6	$175.42	9.204%	$191.5657	$191.57	$191.55	$191.60
Purchase #7	$42.90	7.838%	$46.2625	$46.26	$46.25	$46.30
7 purchase totals =	$913.04		$991.1284	$991.13	$991.15	$991.20