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	$112.91	6.288%	$120.0098	$120.01	$120.00	$120.00
Purchase #2	$174.27	11.776%	$194.792	$194.79	$194.80	$194.80
Purchase #3	$72.27	13.538%	$82.0539	$82.05	$82.05	$82.10
Purchase #4	$29.70	4.239%	$30.959	$30.96	$30.95	$31.00
Purchase #5	$16.73	12.283%	$18.7849	$18.78	$18.80	$18.80
Purchase #6	$42.89	5.677%	$45.3249	$45.32	$45.30	$45.30
Purchase #7	$33.32	12.497%	$37.484	$37.48	$37.50	$37.50
7 purchase totals =	$482.09		$529.4085	$529.39	$529.40	$529.50