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	$146.95	3.349%	$151.8714	$151.87	$151.85	$151.90
Purchase #2	$196.49	4.754%	$205.8311	$205.83	$205.85	$205.80
Purchase #3	$31.34	13.402%	$35.5402	$35.54	$35.55	$35.50
Purchase #4	$185.35	5.354%	$195.2736	$195.27	$195.25	$195.30
Purchase #5	$92.81	7.565%	$99.8311	$99.83	$99.85	$99.80
Purchase #6	$46.77	3.333%	$48.3288	$48.33	$48.35	$48.30
Purchase #7	$239.94	5.706%	$253.631	$253.63	$253.65	$253.60
7 purchase totals =	$939.65		$990.3072	$990.30	$990.35	$990.20