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	$27.75	3.514%	$28.7251	$28.73	$28.75	$28.70
Purchase #2	$179.99	5.649%	$190.1576	$190.16	$190.15	$190.20
Purchase #3	$46.76	7.401%	$50.2207	$50.22	$50.20	$50.20
Purchase #4	$76.96	12.804%	$86.814	$86.81	$86.80	$86.80
Purchase #5	$146.37	5.541%	$154.4804	$154.48	$154.50	$154.50
Purchase #6	$100.88	8.107%	$109.0583	$109.06	$109.05	$109.10
Purchase #7	$55.85	5.772%	$59.0737	$59.07	$59.05	$59.10
7 purchase totals =	$634.56		$678.5298	$678.53	$678.50	$678.60