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	$176.45	3.821%	$183.1922	$183.19	$183.20	$183.20
Purchase #2	$245.71	11.275%	$273.4138	$273.41	$273.40	$273.40
Purchase #3	$103.54	4.570%	$108.2718	$108.27	$108.25	$108.30
Purchase #4	$76.98	8.328%	$83.3909	$83.39	$83.40	$83.40
Purchase #5	$181.89	7.836%	$196.1429	$196.14	$196.15	$196.10
Purchase #6	$124.33	10.215%	$137.0303	$137.03	$137.05	$137.00
Purchase #7	$106.56	4.240%	$111.0781	$111.08	$111.10	$111.10
7 purchase totals =	$1,015.46		$1,092.5200	$1,092.51	$1,092.55	$1,092.50