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	$112.35	7.732%	$121.0369	$121.04	$121.05	$121.00
Purchase #2	$134.86	13.227%	$152.6979	$152.70	$152.70	$152.70
Purchase #3	$53.30	6.170%	$56.5886	$56.59	$56.60	$56.60
Purchase #4	$79.50	12.138%	$89.1497	$89.15	$89.15	$89.10
Purchase #5	$91.91	3.244%	$94.8916	$94.89	$94.90	$94.90
Purchase #6	$215.41	3.228%	$222.3634	$222.36	$222.35	$222.40
Purchase #7	$35.70	3.605%	$36.987	$36.99	$37.00	$37.00
7 purchase totals =	$723.03		$773.7151	$773.72	$773.75	$773.70