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	$51.60	6.513%	$54.9607	$54.96	$54.95	$55.00
Purchase #2	$38.51	13.579%	$43.7393	$43.74	$43.75	$43.70
Purchase #3	$235.27	12.867%	$265.5422	$265.54	$265.55	$265.50
Purchase #4	$89.33	7.378%	$95.9208	$95.92	$95.90	$95.90
Purchase #5	$20.95	4.352%	$21.8617	$21.86	$21.85	$21.90
Purchase #6	$236.43	13.315%	$267.9107	$267.91	$267.90	$267.90
Purchase #7	$70.31	12.798%	$79.3083	$79.31	$79.30	$79.30
7 purchase totals =	$742.40		$829.2437	$829.24	$829.20	$829.20