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	$87.28	8.630%	$94.8123	$94.81	$94.80	$94.80
Purchase #2	$243.32	9.224%	$265.7638	$265.76	$265.75	$265.80
Purchase #3	$90.66	12.269%	$101.7831	$101.78	$101.80	$101.80
Purchase #4	$66.36	8.434%	$71.9568	$71.96	$71.95	$72.00
Purchase #5	$144.91	13.717%	$164.7873	$164.79	$164.80	$164.80
Purchase #6	$241.52	3.265%	$249.4056	$249.41	$249.40	$249.40
Purchase #7	$223.50	8.662%	$242.8596	$242.86	$242.85	$242.90
7 purchase totals =	$1,097.55		$1,191.3685	$1,191.37	$1,191.35	$1,191.50