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	$27.86	9.292%	$30.4488	$30.45	$30.45	$30.40
Purchase #2	$146.48	3.358%	$151.3988	$151.40	$151.40	$151.40
Purchase #3	$130.71	8.210%	$141.4413	$141.44	$141.45	$141.40
Purchase #4	$107.87	8.780%	$117.341	$117.34	$117.35	$117.30
Purchase #5	$51.82	6.185%	$55.0251	$55.03	$55.05	$55.00
Purchase #6	$81.88	10.799%	$90.7222	$90.72	$90.70	$90.70
Purchase #7	$159.70	9.404%	$174.7182	$174.72	$174.70	$174.70
7 purchase totals =	$706.32		$761.0954	$761.10	$761.10	$760.90