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	$55.41	10.144%	$61.0308	$61.03	$61.05	$61.00
Purchase #2	$44.31	6.836%	$47.339	$47.34	$47.35	$47.30
Purchase #3	$46.64	9.189%	$50.9257	$50.93	$50.95	$50.90
Purchase #4	$66.82	5.338%	$70.3869	$70.39	$70.40	$70.40
Purchase #5	$123.57	3.732%	$128.1816	$128.18	$128.20	$128.20
Purchase #6	$17.30	10.678%	$19.1473	$19.15	$19.15	$19.10
Purchase #7	$162.69	3.460%	$168.3191	$168.32	$168.30	$168.30
7 purchase totals =	$516.74		$545.3304	$545.34	$545.40	$545.20