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	$178.59	5.290%	$188.0374	$188.04	$188.05	$188.00
Purchase #2	$75.47	3.404%	$78.039	$78.04	$78.05	$78.00
Purchase #3	$29.76	10.633%	$32.9244	$32.92	$32.90	$32.90
Purchase #4	$29.47	6.424%	$31.3632	$31.36	$31.35	$31.40
Purchase #5	$106.32	6.188%	$112.8991	$112.90	$112.90	$112.90
Purchase #6	$35.71	11.371%	$39.7706	$39.77	$39.75	$39.80
Purchase #7	$90.44	8.298%	$97.9447	$97.94	$97.95	$97.90
7 purchase totals =	$545.76		$580.9784	$580.97	$580.95	$580.90