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	$31.84	4.454%	$33.2582	$33.26	$33.25	$33.30
Purchase #2	$104.37	6.563%	$111.2198	$111.22	$111.20	$111.20
Purchase #3	$188.52	12.108%	$211.346	$211.35	$211.35	$211.30
Purchase #4	$130.90	6.103%	$138.8888	$138.89	$138.90	$138.90
Purchase #5	$56.27	11.126%	$62.5306	$62.53	$62.55	$62.50
Purchase #6	$190.74	13.324%	$216.1542	$216.15	$216.15	$216.20
Purchase #7	$123.57	6.440%	$131.5279	$131.53	$131.55	$131.50
7 purchase totals =	$826.21		$904.9255	$904.93	$904.95	$904.90