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	$32.38	3.198%	$33.4155	$33.42	$33.40	$33.40
Purchase #2	$62.75	6.689%	$66.9473	$66.95	$66.95	$66.90
Purchase #3	$86.44	8.364%	$93.6698	$93.67	$93.65	$93.70
Purchase #4	$49.69	10.315%	$54.8155	$54.82	$54.80	$54.80
Purchase #5	$174.71	12.415%	$196.4002	$196.40	$196.40	$196.40
Purchase #6	$125.96	4.113%	$131.1407	$131.14	$131.15	$131.10
Purchase #7	$73.41	12.282%	$82.4262	$82.43	$82.45	$82.40
7 purchase totals =	$605.34		$658.8152	$658.83	$658.80	$658.70