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	$25.94	6.490%	$27.6235	$27.62	$27.60	$27.60
Purchase #2	$158.70	13.620%	$180.3149	$180.31	$180.30	$180.30
Purchase #3	$98.67	4.524%	$103.1338	$103.13	$103.15	$103.10
Purchase #4	$215.79	3.483%	$223.306	$223.31	$223.30	$223.30
Purchase #5	$35.96	4.345%	$37.5225	$37.52	$37.50	$37.50
Purchase #6	$214.91	11.164%	$238.9026	$238.90	$238.90	$238.90
Purchase #7	$221.63	3.128%	$228.5626	$228.56	$228.55	$228.60
7 purchase totals =	$971.60		$1,039.3659	$1,039.35	$1,039.30	$1,039.30