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	$118.30	4.729%	$123.8944	$123.89	$123.90	$123.90
Purchase #2	$160.32	7.512%	$172.3632	$172.36	$172.35	$172.40
Purchase #3	$31.54	12.648%	$35.5292	$35.53	$35.55	$35.50
Purchase #4	$145.89	7.538%	$156.8872	$156.89	$156.90	$156.90
Purchase #5	$5.66	3.783%	$5.8741	$5.87	$5.85	$5.90
Purchase #6	$171.37	11.217%	$190.5926	$190.59	$190.60	$190.60
Purchase #7	$132.87	10.648%	$147.018	$147.02	$147.00	$147.00
7 purchase totals =	$765.95		$832.1587	$832.15	$832.15	$832.20