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	$204.39	12.383%	$229.6996	$229.70	$229.70	$229.70
Purchase #2	$42.43	6.630%	$45.2431	$45.24	$45.25	$45.20
Purchase #3	$128.47	3.751%	$133.2889	$133.29	$133.30	$133.30
Purchase #4	$124.96	11.550%	$139.3929	$139.39	$139.40	$139.40
Purchase #5	$152.59	10.708%	$168.9293	$168.93	$168.95	$168.90
Purchase #6	$115.39	10.423%	$127.4171	$127.42	$127.40	$127.40
Purchase #7	$193.67	10.395%	$213.802	$213.80	$213.80	$213.80
7 purchase totals =	$961.90		$1,057.7729	$1,057.77	$1,057.80	$1,057.70