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	$35.44	10.412%	$39.13	$39.13	$39.15	$39.10
Purchase #2	$109.77	9.813%	$120.5417	$120.54	$120.55	$120.50
Purchase #3	$91.81	3.394%	$94.926	$94.93	$94.95	$94.90
Purchase #4	$216.70	7.199%	$232.3002	$232.30	$232.30	$232.30
Purchase #5	$102.86	8.402%	$111.5023	$111.50	$111.50	$111.50
Purchase #6	$100.81	10.390%	$111.2842	$111.28	$111.30	$111.30
Purchase #7	$91.40	5.263%	$96.2104	$96.21	$96.20	$96.20
7 purchase totals =	$748.79		$805.8948	$805.89	$805.95	$805.80