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	$88.33	13.360%	$100.1309	$100.13	$100.15	$100.10
Purchase #2	$138.50	5.433%	$146.0247	$146.02	$146.00	$146.00
Purchase #3	$129.43	11.299%	$144.0543	$144.05	$144.05	$144.10
Purchase #4	$203.32	3.780%	$211.0055	$211.01	$211.00	$211.00
Purchase #5	$46.47	12.218%	$52.1477	$52.15	$52.15	$52.10
Purchase #6	$87.93	13.643%	$99.9263	$99.93	$99.95	$99.90
Purchase #7	$114.32	4.568%	$119.5421	$119.54	$119.55	$119.50
7 purchase totals =	$808.30		$872.8315	$872.83	$872.85	$872.70