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	$31.88	4.764%	$33.3988	$33.40	$33.40	$33.40
Purchase #2	$94.59	10.105%	$104.1483	$104.15	$104.15	$104.10
Purchase #3	$106.73	8.824%	$116.1479	$116.15	$116.15	$116.10
Purchase #4	$131.38	6.168%	$139.4835	$139.48	$139.50	$139.50
Purchase #5	$19.73	11.374%	$21.9741	$21.97	$21.95	$22.00
Purchase #6	$127.49	6.742%	$136.0854	$136.09	$136.10	$136.10
Purchase #7	$212.83	7.463%	$228.7135	$228.71	$228.70	$228.70
7 purchase totals =	$724.63		$779.9515	$779.95	$779.95	$779.90