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	$75.46	6.485%	$80.3536	$80.35	$80.35	$80.40
Purchase #2	$56.57	4.240%	$58.9686	$58.97	$58.95	$59.00
Purchase #3	$132.31	3.487%	$136.9236	$136.92	$136.90	$136.90
Purchase #4	$42.48	10.386%	$46.892	$46.89	$46.90	$46.90
Purchase #5	$29.99	7.802%	$32.3298	$32.33	$32.35	$32.30
Purchase #6	$77.87	10.848%	$86.3173	$86.32	$86.30	$86.30
Purchase #7	$31.35	7.187%	$33.6031	$33.60	$33.60	$33.60
7 purchase totals =	$446.03		$475.3880	$475.38	$475.35	$475.40