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	$31.82	5.821%	$33.6722	$33.67	$33.65	$33.70
Purchase #2	$7.84	7.140%	$8.3998	$8.40	$8.40	$8.40
Purchase #3	$95.91	4.601%	$100.3228	$100.32	$100.30	$100.30
Purchase #4	$216.30	3.173%	$223.1632	$223.16	$223.15	$223.20
Purchase #5	$244.90	10.555%	$270.7492	$270.75	$270.75	$270.70
Purchase #6	$71.69	12.286%	$80.4978	$80.50	$80.50	$80.50
Purchase #7	$59.80	11.507%	$66.6812	$66.68	$66.70	$66.70
7 purchase totals =	$728.26		$783.4862	$783.48	$783.45	$783.50