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	$209.92	5.801%	$222.0975	$222.10	$222.10	$222.10
Purchase #2	$111.50	7.521%	$119.8859	$119.89	$119.90	$119.90
Purchase #3	$81.25	12.375%	$91.3047	$91.30	$91.30	$91.30
Purchase #4	$44.31	3.485%	$45.8542	$45.85	$45.85	$45.90
Purchase #5	$65.74	12.854%	$74.1902	$74.19	$74.20	$74.20
Purchase #6	$162.54	5.271%	$171.1075	$171.11	$171.10	$171.10
Purchase #7	$120.90	9.827%	$132.7808	$132.78	$132.80	$132.80
7 purchase totals =	$796.16		$857.2208	$857.22	$857.25	$857.30