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	$27.83	3.258%	$28.7367	$28.74	$28.75	$28.70
Purchase #2	$244.26	7.238%	$261.9395	$261.94	$261.95	$261.90
Purchase #3	$175.45	6.489%	$186.835	$186.84	$186.85	$186.80
Purchase #4	$136.89	3.232%	$141.3143	$141.31	$141.30	$141.30
Purchase #5	$42.92	8.467%	$46.554	$46.55	$46.55	$46.60
Purchase #6	$40.31	5.658%	$42.5907	$42.59	$42.60	$42.60
Purchase #7	$204.77	13.793%	$233.0139	$233.01	$233.00	$233.00
7 purchase totals =	$872.43		$940.9841	$940.98	$941.00	$940.90