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	$82.78	10.535%	$91.5009	$91.50	$91.50	$91.50
Purchase #2	$171.71	5.358%	$180.9102	$180.91	$180.90	$180.90
Purchase #3	$73.94	8.511%	$80.233	$80.23	$80.25	$80.20
Purchase #4	$167.93	6.340%	$178.5768	$178.58	$178.60	$178.60
Purchase #5	$211.78	11.827%	$236.8272	$236.83	$236.85	$236.80
Purchase #6	$243.60	13.180%	$275.7065	$275.71	$275.70	$275.70
Purchase #7	$64.83	8.175%	$70.1299	$70.13	$70.15	$70.10
7 purchase totals =	$1,016.57		$1,113.8845	$1,113.89	$1,113.95	$1,113.80