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	$53.51	13.439%	$60.7012	$60.70	$60.70	$60.70
Purchase #2	$41.96	11.647%	$46.8471	$46.85	$46.85	$46.80
Purchase #3	$30.70	9.413%	$33.5898	$33.59	$33.60	$33.60
Purchase #4	$96.36	9.686%	$105.6934	$105.69	$105.70	$105.70
Purchase #5	$84.36	6.219%	$89.6063	$89.61	$89.60	$89.60
Purchase #6	$36.91	13.564%	$41.9165	$41.92	$41.90	$41.90
Purchase #7	$84.71	9.206%	$92.5084	$92.51	$92.50	$92.50
7 purchase totals =	$428.51		$470.8627	$470.87	$470.85	$470.80