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	$97.72	12.689%	$110.1197	$110.12	$110.10	$110.10
Purchase #2	$31.84	8.804%	$34.6432	$34.64	$34.65	$34.60
Purchase #3	$102.54	8.495%	$111.2508	$111.25	$111.25	$111.30
Purchase #4	$250.78	13.595%	$284.8735	$284.87	$284.85	$284.90
Purchase #5	$29.53	4.369%	$30.8202	$30.82	$30.80	$30.80
Purchase #6	$250.39	12.309%	$281.2105	$281.21	$281.20	$281.20
Purchase #7	$147.79	12.505%	$166.2711	$166.27	$166.25	$166.30
7 purchase totals =	$910.59		$1,019.1890	$1,019.18	$1,019.10	$1,019.20