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	$120.63	13.196%	$136.5483	$136.55	$136.55	$136.50
Purchase #2	$184.25	6.496%	$196.2189	$196.22	$196.20	$196.20
Purchase #3	$94.57	4.174%	$98.5174	$98.52	$98.50	$98.50
Purchase #4	$201.27	8.251%	$217.8768	$217.88	$217.90	$217.90
Purchase #5	$89.36	11.179%	$99.3496	$99.35	$99.35	$99.30
Purchase #6	$211.77	10.565%	$234.1435	$234.14	$234.15	$234.10
Purchase #7	$118.86	9.322%	$129.9401	$129.94	$129.95	$129.90
7 purchase totals =	$1,020.71		$1,112.5946	$1,112.60	$1,112.60	$1,112.40