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	$150.83	13.585%	$171.3203	$171.32	$171.30	$171.30
Purchase #2	$99.80	9.688%	$109.4686	$109.47	$109.45	$109.50
Purchase #3	$149.38	11.269%	$166.2136	$166.21	$166.20	$166.20
Purchase #4	$13.99	9.422%	$15.3081	$15.31	$15.30	$15.30
Purchase #5	$14.79	3.642%	$15.3287	$15.33	$15.35	$15.30
Purchase #6	$238.92	4.578%	$249.8578	$249.86	$249.85	$249.90
Purchase #7	$79.50	7.118%	$85.1588	$85.16	$85.15	$85.20
7 purchase totals =	$747.21		$812.6559	$812.66	$812.60	$812.70