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	$91.92	8.818%	$100.0255	$100.03	$100.05	$100.00
Purchase #2	$31.39	6.419%	$33.4049	$33.40	$33.40	$33.40
Purchase #3	$98.68	10.784%	$109.3217	$109.32	$109.30	$109.30
Purchase #4	$59.98	4.138%	$62.462	$62.46	$62.45	$62.50
Purchase #5	$231.30	4.794%	$242.3885	$242.39	$242.40	$242.40
Purchase #6	$183.98	8.250%	$199.1584	$199.16	$199.15	$199.20
Purchase #7	$233.72	10.193%	$257.5431	$257.54	$257.55	$257.50
7 purchase totals =	$930.97		$1,004.3041	$1,004.30	$1,004.30	$1,004.30