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	$222.31	11.459%	$247.7845	$247.78	$247.80	$247.80
Purchase #2	$30.70	4.820%	$32.1797	$32.18	$32.20	$32.20
Purchase #3	$88.34	5.147%	$92.8869	$92.89	$92.90	$92.90
Purchase #4	$38.52	9.747%	$42.2745	$42.27	$42.25	$42.30
Purchase #5	$33.41	7.130%	$35.7921	$35.79	$35.80	$35.80
Purchase #6	$229.37	6.834%	$245.0451	$245.05	$245.05	$245.00
Purchase #7	$122.40	9.417%	$133.9264	$133.93	$133.95	$133.90
7 purchase totals =	$765.05		$829.8892	$829.89	$829.95	$829.90