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	$36.75	10.231%	$40.5099	$40.51	$40.50	$40.50
Purchase #2	$160.98	13.428%	$182.5964	$182.60	$182.60	$182.60
Purchase #3	$181.80	5.344%	$191.5154	$191.52	$191.50	$191.50
Purchase #4	$100.32	5.203%	$105.5396	$105.54	$105.55	$105.50
Purchase #5	$71.56	8.452%	$77.6083	$77.61	$77.60	$77.60
Purchase #6	$164.86	10.106%	$181.5208	$181.52	$181.50	$181.50
Purchase #7	$219.85	10.342%	$242.5869	$242.59	$242.60	$242.60
7 purchase totals =	$936.12		$1,021.8773	$1,021.89	$1,021.85	$1,021.80