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	$80.36	11.413%	$89.5315	$89.53	$89.55	$89.50
Purchase #2	$235.49	13.688%	$267.7239	$267.72	$267.70	$267.70
Purchase #3	$180.71	4.430%	$188.7155	$188.72	$188.70	$188.70
Purchase #4	$84.87	11.151%	$94.3339	$94.33	$94.35	$94.30
Purchase #5	$40.82	6.520%	$43.4815	$43.48	$43.50	$43.50
Purchase #6	$49.67	6.404%	$52.8509	$52.85	$52.85	$52.90
Purchase #7	$144.39	9.147%	$157.5974	$157.60	$157.60	$157.60
7 purchase totals =	$816.31		$894.2346	$894.23	$894.25	$894.20