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	$73.89	11.238%	$82.1938	$82.19	$82.20	$82.20
Purchase #2	$232.82	4.154%	$242.4913	$242.49	$242.50	$242.50
Purchase #3	$86.72	12.178%	$97.2808	$97.28	$97.30	$97.30
Purchase #4	$71.30	8.668%	$77.4803	$77.48	$77.50	$77.50
Purchase #5	$198.58	11.123%	$220.6681	$220.67	$220.65	$220.70
Purchase #6	$67.74	5.347%	$71.3621	$71.36	$71.35	$71.40
Purchase #7	$52.37	11.259%	$58.2663	$58.27	$58.25	$58.30
7 purchase totals =	$783.42		$849.7427	$849.74	$849.75	$849.90