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	$184.26	11.421%	$205.3043	$205.30	$205.30	$205.30
Purchase #2	$151.89	10.538%	$167.8962	$167.90	$167.90	$167.90
Purchase #3	$166.96	12.866%	$188.4411	$188.44	$188.45	$188.40
Purchase #4	$172.34	11.220%	$191.6765	$191.68	$191.70	$191.70
Purchase #5	$70.38	4.492%	$73.5415	$73.54	$73.55	$73.50
Purchase #6	$66.56	7.786%	$71.7424	$71.74	$71.75	$71.70
Purchase #7	$18.45	9.872%	$20.2714	$20.27	$20.25	$20.30
7 purchase totals =	$830.84		$918.8734	$918.87	$918.90	$918.80