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	$89.54	3.224%	$92.4268	$92.43	$92.45	$92.40
Purchase #2	$223.56	9.708%	$245.2632	$245.26	$245.25	$245.30
Purchase #3	$91.72	9.114%	$100.0794	$100.08	$100.10	$100.10
Purchase #4	$96.73	7.317%	$103.8077	$103.81	$103.80	$103.80
Purchase #5	$164.73	13.582%	$187.1036	$187.10	$187.10	$187.10
Purchase #6	$134.95	5.564%	$142.4586	$142.46	$142.45	$142.50
Purchase #7	$36.37	11.732%	$40.6369	$40.64	$40.65	$40.60
7 purchase totals =	$837.60		$911.7762	$911.78	$911.80	$911.80