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	$67.57	5.780%	$71.4755	$71.48	$71.50	$71.50
Purchase #2	$35.80	10.494%	$39.5569	$39.56	$39.55	$39.60
Purchase #3	$190.67	10.374%	$210.4501	$210.45	$210.45	$210.50
Purchase #4	$146.58	13.217%	$165.9535	$165.95	$165.95	$166.00
Purchase #5	$171.81	11.385%	$191.3706	$191.37	$191.35	$191.40
Purchase #6	$146.94	4.586%	$153.6787	$153.68	$153.70	$153.70
Purchase #7	$36.32	4.301%	$37.8821	$37.88	$37.90	$37.90
7 purchase totals =	$795.69		$870.3674	$870.37	$870.40	$870.60