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	$61.46	3.370%	$63.5312	$63.53	$63.55	$63.50
Purchase #2	$172.26	8.393%	$186.7178	$186.72	$186.70	$186.70
Purchase #3	$84.89	7.809%	$91.5191	$91.52	$91.50	$91.50
Purchase #4	$164.63	6.556%	$175.4231	$175.42	$175.40	$175.40
Purchase #5	$217.39	7.390%	$233.4551	$233.46	$233.45	$233.50
Purchase #6	$18.33	5.547%	$19.3468	$19.35	$19.35	$19.30
Purchase #7	$223.40	11.825%	$249.8171	$249.82	$249.80	$249.80
7 purchase totals =	$942.36		$1,019.8102	$1,019.82	$1,019.75	$1,019.70