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	$18.81	8.775%	$20.4606	$20.46	$20.45	$20.50
Purchase #2	$75.33	13.253%	$85.3135	$85.31	$85.30	$85.30
Purchase #3	$26.48	3.646%	$27.4455	$27.45	$27.45	$27.40
Purchase #4	$213.83	4.648%	$223.7688	$223.77	$223.75	$223.80
Purchase #5	$118.92	4.178%	$123.8885	$123.89	$123.90	$123.90
Purchase #6	$248.25	9.472%	$271.7642	$271.76	$271.75	$271.80
Purchase #7	$38.64	4.212%	$40.2675	$40.27	$40.25	$40.30
7 purchase totals =	$740.26		$792.9086	$792.91	$792.85	$793.00