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	$155.43	10.472%	$171.7066	$171.71	$171.70	$171.70
Purchase #2	$111.95	6.764%	$119.5223	$119.52	$119.50	$119.50
Purchase #3	$73.67	11.770%	$82.341	$82.34	$82.35	$82.30
Purchase #4	$115.78	13.366%	$131.2552	$131.26	$131.25	$131.30
Purchase #5	$154.73	13.439%	$175.5242	$175.52	$175.50	$175.50
Purchase #6	$232.36	7.251%	$249.2084	$249.21	$249.20	$249.20
Purchase #7	$51.56	7.259%	$55.3027	$55.30	$55.30	$55.30
7 purchase totals =	$895.48		$984.8604	$984.86	$984.80	$984.80