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	$104.98	3.810%	$108.9797	$108.98	$109.00	$109.00
Purchase #2	$249.94	9.315%	$273.2219	$273.22	$273.20	$273.20
Purchase #3	$116.86	12.320%	$131.2572	$131.26	$131.25	$131.30
Purchase #4	$50.59	12.332%	$56.8288	$56.83	$56.85	$56.80
Purchase #5	$67.98	4.139%	$70.7937	$70.79	$70.80	$70.80
Purchase #6	$143.91	3.768%	$149.3325	$149.33	$149.35	$149.30
Purchase #7	$105.84	6.317%	$112.5259	$112.53	$112.55	$112.50
7 purchase totals =	$840.10		$902.9397	$902.94	$903.00	$902.90