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	$211.31	5.585%	$223.1117	$223.11	$223.10	$223.10
Purchase #2	$81.45	6.123%	$86.4372	$86.44	$86.45	$86.40
Purchase #3	$7.49	10.559%	$8.2809	$8.28	$8.30	$8.30
Purchase #4	$214.81	11.513%	$239.5411	$239.54	$239.55	$239.50
Purchase #5	$218.46	11.204%	$242.9363	$242.94	$242.95	$242.90
Purchase #6	$123.47	12.592%	$139.0173	$139.02	$139.00	$139.00
Purchase #7	$89.60	11.443%	$99.8529	$99.85	$99.85	$99.90
7 purchase totals =	$946.59		$1,039.1774	$1,039.18	$1,039.20	$1,039.10