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	$77.27	13.751%	$87.8954	$87.90	$87.90	$87.90
Purchase #2	$45.68	4.673%	$47.8146	$47.81	$47.80	$47.80
Purchase #3	$123.29	10.740%	$136.5313	$136.53	$136.55	$136.50
Purchase #4	$140.88	5.617%	$148.7932	$148.79	$148.80	$148.80
Purchase #5	$103.72	3.578%	$107.4311	$107.43	$107.45	$107.40
Purchase #6	$162.36	6.380%	$172.7186	$172.72	$172.70	$172.70
Purchase #7	$139.50	7.637%	$150.1536	$150.15	$150.15	$150.20
7 purchase totals =	$792.70		$851.3378	$851.33	$851.35	$851.30