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	$248.29	10.125%	$273.4294	$273.43	$273.45	$273.40
Purchase #2	$90.33	7.265%	$96.8925	$96.89	$96.90	$96.90
Purchase #3	$156.59	12.354%	$175.9351	$175.94	$175.95	$175.90
Purchase #4	$13.48	13.644%	$15.3192	$15.32	$15.30	$15.30
Purchase #5	$56.65	8.108%	$61.2432	$61.24	$61.25	$61.20
Purchase #6	$104.40	7.542%	$112.2738	$112.27	$112.25	$112.30
Purchase #7	$119.33	9.538%	$130.7117	$130.71	$130.70	$130.70
7 purchase totals =	$789.07		$865.8049	$865.80	$865.80	$865.70