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	$81.88	9.665%	$89.7937	$89.79	$89.80	$89.80
Purchase #2	$43.70	8.243%	$47.3022	$47.30	$47.30	$47.30
Purchase #3	$146.34	8.845%	$159.2838	$159.28	$159.30	$159.30
Purchase #4	$173.26	13.552%	$196.7402	$196.74	$196.75	$196.70
Purchase #5	$13.80	8.578%	$14.9838	$14.98	$15.00	$15.00
Purchase #6	$66.54	7.219%	$71.3435	$71.34	$71.35	$71.30
Purchase #7	$191.91	11.188%	$213.3809	$213.38	$213.40	$213.40
7 purchase totals =	$717.43		$792.8281	$792.81	$792.90	$792.80