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	$146.43	10.182%	$161.3395	$161.34	$161.35	$161.30
Purchase #2	$87.48	10.260%	$96.4554	$96.46	$96.45	$96.50
Purchase #3	$73.57	12.400%	$82.6927	$82.69	$82.70	$82.70
Purchase #4	$71.95	12.541%	$80.9732	$80.97	$80.95	$81.00
Purchase #5	$158.76	7.777%	$171.1068	$171.11	$171.10	$171.10
Purchase #6	$71.46	12.413%	$80.3303	$80.33	$80.35	$80.30
Purchase #7	$87.49	3.246%	$90.3299	$90.33	$90.35	$90.30
7 purchase totals =	$697.14		$763.2278	$763.23	$763.25	$763.20