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	$131.93	8.827%	$143.5755	$143.58	$143.60	$143.60
Purchase #2	$217.60	12.732%	$245.3048	$245.30	$245.30	$245.30
Purchase #3	$227.56	13.596%	$258.4991	$258.50	$258.50	$258.50
Purchase #4	$41.42	12.331%	$46.5275	$46.53	$46.55	$46.50
Purchase #5	$35.81	4.764%	$37.516	$37.52	$37.50	$37.50
Purchase #6	$67.64	5.709%	$71.5016	$71.50	$71.50	$71.50
Purchase #7	$19.35	6.281%	$20.5654	$20.57	$20.55	$20.60
7 purchase totals =	$741.31		$823.4899	$823.50	$823.50	$823.50