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	$233.65	13.110%	$264.2815	$264.28	$264.30	$264.30
Purchase #2	$80.62	10.674%	$89.2254	$89.23	$89.25	$89.20
Purchase #3	$31.36	6.785%	$33.4878	$33.49	$33.50	$33.50
Purchase #4	$127.26	12.584%	$143.2744	$143.27	$143.25	$143.30
Purchase #5	$210.73	12.834%	$237.7751	$237.78	$237.80	$237.80
Purchase #6	$68.66	12.515%	$77.2528	$77.25	$77.25	$77.30
Purchase #7	$130.83	10.850%	$145.0251	$145.03	$145.05	$145.00
7 purchase totals =	$883.11		$990.3221	$990.33	$990.40	$990.40