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	$89.25	3.463%	$92.3407	$92.34	$92.35	$92.30
Purchase #2	$65.54	3.148%	$67.6032	$67.60	$67.60	$67.60
Purchase #3	$54.69	10.562%	$60.4664	$60.47	$60.45	$60.50
Purchase #4	$65.35	13.654%	$74.2729	$74.27	$74.25	$74.30
Purchase #5	$131.38	7.712%	$141.512	$141.51	$141.50	$141.50
Purchase #6	$102.83	8.143%	$111.2034	$111.20	$111.20	$111.20
Purchase #7	$207.27	9.190%	$226.3181	$226.32	$226.30	$226.30
7 purchase totals =	$716.31		$773.7167	$773.71	$773.65	$773.70