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	$143.88	4.826%	$150.8236	$150.82	$150.80	$150.80
Purchase #2	$89.31	9.632%	$97.9123	$97.91	$97.90	$97.90
Purchase #3	$106.69	7.285%	$114.4624	$114.46	$114.45	$114.50
Purchase #4	$97.56	13.192%	$110.4301	$110.43	$110.45	$110.40
Purchase #5	$63.41	5.590%	$66.9546	$66.95	$66.95	$67.00
Purchase #6	$88.88	10.115%	$97.8702	$97.87	$97.85	$97.90
Purchase #7	$31.52	5.559%	$33.2722	$33.27	$33.25	$33.30
7 purchase totals =	$621.25		$671.7254	$671.71	$671.65	$671.80