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	$235.31	12.518%	$264.7661	$264.77	$264.75	$264.80
Purchase #2	$53.54	10.449%	$59.1344	$59.13	$59.15	$59.10
Purchase #3	$40.70	5.292%	$42.8538	$42.85	$42.85	$42.90
Purchase #4	$214.70	7.727%	$231.2899	$231.29	$231.30	$231.30
Purchase #5	$222.33	10.599%	$245.8948	$245.89	$245.90	$245.90
Purchase #6	$84.33	5.709%	$89.1444	$89.14	$89.15	$89.10
Purchase #7	$199.88	8.549%	$216.9677	$216.97	$216.95	$217.00
7 purchase totals =	$1,050.79		$1,150.0511	$1,150.04	$1,150.05	$1,150.10