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	$202.59	9.662%	$222.1642	$222.16	$222.15	$222.20
Purchase #2	$174.58	12.754%	$196.8459	$196.85	$196.85	$196.80
Purchase #3	$20.91	5.329%	$22.0243	$22.02	$22.00	$22.00
Purchase #4	$42.28	6.467%	$45.0142	$45.01	$45.00	$45.00
Purchase #5	$91.68	3.389%	$94.787	$94.79	$94.80	$94.80
Purchase #6	$59.79	10.165%	$65.8677	$65.87	$65.85	$65.90
Purchase #7	$105.65	13.691%	$120.1145	$120.11	$120.10	$120.10
7 purchase totals =	$697.48		$766.8178	$766.81	$766.75	$766.80