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	$16.37	10.124%	$18.0273	$18.03	$18.05	$18.00
Purchase #2	$178.44	11.654%	$199.2354	$199.24	$199.25	$199.20
Purchase #3	$41.66	11.496%	$46.4492	$46.45	$46.45	$46.40
Purchase #4	$249.47	6.540%	$265.7853	$265.79	$265.80	$265.80
Purchase #5	$242.46	13.320%	$274.7557	$274.76	$274.75	$274.80
Purchase #6	$112.42	13.272%	$127.3404	$127.34	$127.35	$127.30
Purchase #7	$162.37	10.798%	$179.9027	$179.90	$179.90	$179.90
7 purchase totals =	$1,003.19		$1,111.4960	$1,111.51	$1,111.55	$1,111.40