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	$213.95	7.106%	$229.1533	$229.15	$229.15	$229.20
Purchase #2	$37.80	11.768%	$42.2483	$42.25	$42.25	$42.20
Purchase #3	$237.78	9.438%	$260.2217	$260.22	$260.20	$260.20
Purchase #4	$158.98	6.109%	$168.6921	$168.69	$168.70	$168.70
Purchase #5	$142.83	5.315%	$150.4214	$150.42	$150.40	$150.40
Purchase #6	$58.80	3.367%	$60.7798	$60.78	$60.80	$60.80
Purchase #7	$67.54	4.121%	$70.3233	$70.32	$70.30	$70.30
7 purchase totals =	$917.68		$981.8399	$981.83	$981.80	$981.80