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	$117.52	11.439%	$130.9631	$130.96	$130.95	$131.00
Purchase #2	$171.56	10.562%	$189.6802	$189.68	$189.70	$189.70
Purchase #3	$211.35	8.544%	$229.4077	$229.41	$229.40	$229.40
Purchase #4	$174.56	4.193%	$181.8793	$181.88	$181.90	$181.90
Purchase #5	$204.97	3.372%	$211.8816	$211.88	$211.90	$211.90
Purchase #6	$82.76	8.659%	$89.9262	$89.93	$89.95	$89.90
Purchase #7	$223.79	13.490%	$253.9793	$253.98	$254.00	$254.00
7 purchase totals =	$1,186.51		$1,287.7174	$1,287.72	$1,287.80	$1,287.80