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	$91.78	8.148%	$99.2582	$99.26	$99.25	$99.30
Purchase #2	$110.97	13.794%	$126.2772	$126.28	$126.30	$126.30
Purchase #3	$158.50	3.874%	$164.6403	$164.64	$164.65	$164.60
Purchase #4	$247.56	13.347%	$280.6018	$280.60	$280.60	$280.60
Purchase #5	$170.44	5.773%	$180.2795	$180.28	$180.30	$180.30
Purchase #6	$81.43	9.507%	$89.1716	$89.17	$89.15	$89.20
Purchase #7	$115.84	12.117%	$129.8763	$129.88	$129.90	$129.90
7 purchase totals =	$976.52		$1,070.1049	$1,070.11	$1,070.15	$1,070.20