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	$174.82	11.233%	$194.4575	$194.46	$194.45	$194.50
Purchase #2	$123.78	5.741%	$130.8862	$130.89	$130.90	$130.90
Purchase #3	$135.31	11.850%	$151.3442	$151.34	$151.35	$151.30
Purchase #4	$56.79	8.755%	$61.762	$61.76	$61.75	$61.80
Purchase #5	$41.75	10.573%	$46.1642	$46.16	$46.15	$46.20
Purchase #6	$223.77	11.703%	$249.9578	$249.96	$249.95	$250.00
Purchase #7	$84.53	8.748%	$91.9247	$91.92	$91.90	$91.90
7 purchase totals =	$840.75		$926.4966	$926.49	$926.45	$926.60