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	$99.47	11.796%	$111.2035	$111.20	$111.20	$111.20
Purchase #2	$196.35	8.810%	$213.6484	$213.65	$213.65	$213.60
Purchase #3	$201.75	10.201%	$222.3305	$222.33	$222.35	$222.30
Purchase #4	$211.31	10.613%	$233.7363	$233.74	$233.75	$233.70
Purchase #5	$149.93	3.342%	$154.9407	$154.94	$154.95	$154.90
Purchase #6	$86.96	3.334%	$89.8592	$89.86	$89.85	$89.90
Purchase #7	$209.33	3.810%	$217.3055	$217.31	$217.30	$217.30
7 purchase totals =	$1,155.10		$1,243.0241	$1,243.03	$1,243.05	$1,242.90