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	$45.63	13.352%	$51.7225	$51.72	$51.70	$51.70
Purchase #2	$79.67	11.645%	$88.9476	$88.95	$88.95	$88.90
Purchase #3	$82.27	3.600%	$85.2317	$85.23	$85.25	$85.20
Purchase #4	$64.80	4.140%	$67.4827	$67.48	$67.50	$67.50
Purchase #5	$61.82	6.827%	$66.0405	$66.04	$66.05	$66.00
Purchase #6	$128.33	12.152%	$143.9247	$143.92	$143.90	$143.90
Purchase #7	$103.90	13.749%	$118.1852	$118.19	$118.20	$118.20
7 purchase totals =	$566.42		$621.5349	$621.53	$621.55	$621.40