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	$188.91	9.128%	$206.1537	$206.15	$206.15	$206.20
Purchase #2	$60.51	6.820%	$64.6368	$64.64	$64.65	$64.60
Purchase #3	$99.83	13.172%	$112.9796	$112.98	$113.00	$113.00
Purchase #4	$39.38	7.507%	$42.3363	$42.34	$42.35	$42.30
Purchase #5	$158.46	3.758%	$164.4149	$164.41	$164.40	$164.40
Purchase #6	$248.90	8.119%	$269.1082	$269.11	$269.10	$269.10
Purchase #7	$233.30	5.420%	$245.9449	$245.94	$245.95	$245.90
7 purchase totals =	$1,029.29		$1,105.5744	$1,105.57	$1,105.60	$1,105.50