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	$116.69	6.180%	$123.9014	$123.90	$123.90	$123.90
Purchase #2	$221.94	9.535%	$243.102	$243.10	$243.10	$243.10
Purchase #3	$164.69	3.645%	$170.693	$170.69	$170.70	$170.70
Purchase #4	$184.93	3.715%	$191.8001	$191.80	$191.80	$191.80
Purchase #5	$194.76	11.350%	$216.8653	$216.87	$216.85	$216.90
Purchase #6	$104.28	13.328%	$118.1784	$118.18	$118.20	$118.20
Purchase #7	$84.60	6.341%	$89.9645	$89.96	$89.95	$90.00
7 purchase totals =	$1,071.89		$1,154.5047	$1,154.50	$1,154.50	$1,154.60