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	$34.59	10.261%	$38.1393	$38.14	$38.15	$38.10
Purchase #2	$87.87	12.719%	$99.0462	$99.05	$99.05	$99.00
Purchase #3	$62.88	7.392%	$67.5281	$67.53	$67.55	$67.50
Purchase #4	$77.30	10.576%	$85.4752	$85.48	$85.50	$85.50
Purchase #5	$77.53	13.570%	$88.0508	$88.05	$88.05	$88.10
Purchase #6	$31.33	8.718%	$34.0613	$34.06	$34.05	$34.10
Purchase #7	$64.27	10.335%	$70.9123	$70.91	$70.90	$70.90
7 purchase totals =	$435.77		$483.2132	$483.22	$483.25	$483.20