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	$16.46	11.194%	$18.3025	$18.30	$18.30	$18.30
Purchase #2	$67.62	6.390%	$71.9409	$71.94	$71.95	$71.90
Purchase #3	$191.33	13.742%	$217.6226	$217.62	$217.60	$217.60
Purchase #4	$89.74	13.298%	$101.6736	$101.67	$101.65	$101.70
Purchase #5	$33.95	10.385%	$37.4757	$37.48	$37.50	$37.50
Purchase #6	$31.48	13.498%	$35.7292	$35.73	$35.75	$35.70
Purchase #7	$219.26	6.670%	$233.8846	$233.88	$233.90	$233.90
7 purchase totals =	$649.84		$716.6291	$716.62	$716.65	$716.60