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	$83.42	9.595%	$91.4241	$91.42	$91.40	$91.40
Purchase #2	$218.64	6.764%	$233.4288	$233.43	$233.45	$233.40
Purchase #3	$43.52	4.268%	$45.3774	$45.38	$45.40	$45.40
Purchase #4	$169.88	10.446%	$187.6257	$187.63	$187.65	$187.60
Purchase #5	$58.58	12.362%	$65.8217	$65.82	$65.80	$65.80
Purchase #6	$191.91	3.514%	$198.6537	$198.65	$198.65	$198.70
Purchase #7	$94.84	3.860%	$98.5008	$98.50	$98.50	$98.50
7 purchase totals =	$860.79		$920.8322	$920.83	$920.85	$920.80