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	$232.52	12.284%	$261.0828	$261.08	$261.10	$261.10
Purchase #2	$230.98	8.477%	$250.5602	$250.56	$250.55	$250.60
Purchase #3	$12.66	8.596%	$13.7483	$13.75	$13.75	$13.70
Purchase #4	$141.89	8.672%	$154.1947	$154.19	$154.20	$154.20
Purchase #5	$194.56	13.251%	$220.3411	$220.34	$220.35	$220.30
Purchase #6	$98.77	12.452%	$111.0688	$111.07	$111.05	$111.10
Purchase #7	$196.72	13.120%	$222.5297	$222.53	$222.55	$222.50
7 purchase totals =	$1,108.10		$1,233.5256	$1,233.52	$1,233.55	$1,233.50