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	$96.28	3.768%	$99.9078	$99.91	$99.90	$99.90
Purchase #2	$223.78	7.372%	$240.2771	$240.28	$240.30	$240.30
Purchase #3	$180.26	4.728%	$188.7827	$188.78	$188.80	$188.80
Purchase #4	$142.90	4.395%	$149.1805	$149.18	$149.20	$149.20
Purchase #5	$57.79	6.204%	$61.3753	$61.38	$61.40	$61.40
Purchase #6	$147.81	9.266%	$161.5061	$161.51	$161.50	$161.50
Purchase #7	$95.77	3.258%	$98.8902	$98.89	$98.90	$98.90
7 purchase totals =	$944.59		$999.9197	$999.93	$1,000.00	$1,000.00