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	$111.26	6.666%	$118.6766	$118.68	$118.70	$118.70
Purchase #2	$91.56	11.760%	$102.3275	$102.33	$102.35	$102.30
Purchase #3	$201.54	12.418%	$226.5672	$226.57	$226.55	$226.60
Purchase #4	$92.78	6.133%	$98.4702	$98.47	$98.45	$98.50
Purchase #5	$167.69	7.846%	$180.847	$180.85	$180.85	$180.80
Purchase #6	$204.60	13.595%	$232.4154	$232.42	$232.40	$232.40
Purchase #7	$80.73	11.275%	$89.8323	$89.83	$89.85	$89.80
7 purchase totals =	$950.16		$1,049.1362	$1,049.15	$1,049.15	$1,049.10