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	$89.73	10.589%	$99.2315	$99.23	$99.25	$99.20
Purchase #2	$126.27	13.765%	$143.6511	$143.65	$143.65	$143.70
Purchase #3	$61.52	4.424%	$64.2416	$64.24	$64.25	$64.20
Purchase #4	$188.78	5.648%	$199.4423	$199.44	$199.45	$199.40
Purchase #5	$203.49	11.472%	$226.8344	$226.83	$226.85	$226.80
Purchase #6	$68.89	7.257%	$73.8893	$73.89	$73.90	$73.90
Purchase #7	$6.63	6.411%	$7.055	$7.06	$7.05	$7.10
7 purchase totals =	$745.31		$814.3452	$814.34	$814.40	$814.30