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	$28.27	4.215%	$29.4616	$29.46	$29.45	$29.50
Purchase #2	$205.85	11.687%	$229.9077	$229.91	$229.90	$229.90
Purchase #3	$118.69	12.223%	$133.1975	$133.20	$133.20	$133.20
Purchase #4	$228.57	7.605%	$245.9527	$245.95	$245.95	$246.00
Purchase #5	$78.92	8.606%	$85.7119	$85.71	$85.70	$85.70
Purchase #6	$96.66	8.482%	$104.8587	$104.86	$104.85	$104.90
Purchase #7	$139.53	3.560%	$144.4973	$144.50	$144.50	$144.50
7 purchase totals =	$896.49		$973.5874	$973.59	$973.55	$973.70