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	$84.65	4.114%	$88.1325	$88.13	$88.15	$88.10
Purchase #2	$82.51	7.267%	$88.506	$88.51	$88.50	$88.50
Purchase #3	$95.38	8.292%	$103.2889	$103.29	$103.30	$103.30
Purchase #4	$143.50	11.729%	$160.3311	$160.33	$160.35	$160.30
Purchase #5	$125.43	4.467%	$131.033	$131.03	$131.05	$131.00
Purchase #6	$96.47	4.156%	$100.4793	$100.48	$100.50	$100.50
Purchase #7	$61.38	4.779%	$64.3134	$64.31	$64.30	$64.30
7 purchase totals =	$689.32		$736.0842	$736.08	$736.15	$736.00