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	$248.82	6.308%	$264.5156	$264.52	$264.50	$264.50
Purchase #2	$142.91	13.640%	$162.4029	$162.40	$162.40	$162.40
Purchase #3	$70.27	8.640%	$76.3413	$76.34	$76.35	$76.30
Purchase #4	$85.61	11.660%	$95.5921	$95.59	$95.60	$95.60
Purchase #5	$236.68	3.148%	$244.1307	$244.13	$244.15	$244.10
Purchase #6	$72.49	9.421%	$79.3193	$79.32	$79.30	$79.30
Purchase #7	$82.99	7.863%	$89.5155	$89.52	$89.50	$89.50
7 purchase totals =	$939.77		$1,011.8174	$1,011.82	$1,011.80	$1,011.70