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	$203.83	11.316%	$226.8954	$226.90	$226.90	$226.90
Purchase #2	$165.51	8.514%	$179.6015	$179.60	$179.60	$179.60
Purchase #3	$108.50	13.391%	$123.0292	$123.03	$123.05	$123.00
Purchase #4	$130.89	4.332%	$136.5602	$136.56	$136.55	$136.60
Purchase #5	$73.47	10.637%	$81.285	$81.29	$81.30	$81.30
Purchase #6	$89.66	12.244%	$100.638	$100.64	$100.65	$100.60
Purchase #7	$183.84	13.843%	$209.289	$209.29	$209.30	$209.30
7 purchase totals =	$955.70		$1,057.2983	$1,057.31	$1,057.35	$1,057.30