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	$89.33	9.526%	$97.8396	$97.84	$97.85	$97.80
Purchase #2	$135.30	9.726%	$148.4593	$148.46	$148.45	$148.50
Purchase #3	$135.62	11.223%	$150.8406	$150.84	$150.85	$150.80
Purchase #4	$240.83	6.429%	$256.313	$256.31	$256.30	$256.30
Purchase #5	$111.69	13.615%	$126.8966	$126.90	$126.90	$126.90
Purchase #6	$140.68	13.723%	$159.9855	$159.99	$160.00	$160.00
Purchase #7	$37.34	11.245%	$41.5389	$41.54	$41.55	$41.50
7 purchase totals =	$890.79		$981.8735	$981.88	$981.90	$981.80