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	$215.53	3.368%	$222.7891	$222.79	$222.80	$222.80
Purchase #2	$160.57	6.584%	$171.1419	$171.14	$171.15	$171.10
Purchase #3	$73.54	10.711%	$81.4169	$81.42	$81.40	$81.40
Purchase #4	$86.81	3.646%	$89.9751	$89.98	$90.00	$90.00
Purchase #5	$151.84	6.506%	$161.7187	$161.72	$161.70	$161.70
Purchase #6	$126.28	8.679%	$137.2398	$137.24	$137.25	$137.20
Purchase #7	$129.41	7.814%	$139.5221	$139.52	$139.50	$139.50
7 purchase totals =	$943.98		$1,003.8036	$1,003.81	$1,003.80	$1,003.70