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	$142.56	3.349%	$147.3343	$147.33	$147.35	$147.30
Purchase #2	$103.48	8.138%	$111.9012	$111.90	$111.90	$111.90
Purchase #3	$124.31	5.507%	$131.1558	$131.16	$131.15	$131.20
Purchase #4	$120.62	13.187%	$136.5262	$136.53	$136.55	$136.50
Purchase #5	$134.76	3.815%	$139.9011	$139.90	$139.90	$139.90
Purchase #6	$34.78	8.868%	$37.8643	$37.86	$37.85	$37.90
Purchase #7	$45.63	10.581%	$50.4581	$50.46	$50.45	$50.50
7 purchase totals =	$706.14		$755.1410	$755.14	$755.15	$755.20