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	$7.69	8.361%	$8.333	$8.33	$8.35	$8.30
Purchase #2	$136.25	12.205%	$152.8793	$152.88	$152.90	$152.90
Purchase #3	$153.79	9.594%	$168.5446	$168.54	$168.55	$168.50
Purchase #4	$136.49	11.683%	$152.4361	$152.44	$152.45	$152.40
Purchase #5	$55.74	12.636%	$62.7833	$62.78	$62.80	$62.80
Purchase #6	$146.94	9.299%	$160.604	$160.60	$160.60	$160.60
Purchase #7	$218.41	6.140%	$231.8204	$231.82	$231.80	$231.80
7 purchase totals =	$855.31		$937.4007	$937.39	$937.45	$937.30