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	$245.85	7.458%	$264.1855	$264.19	$264.20	$264.20
Purchase #2	$42.50	4.437%	$44.3857	$44.39	$44.40	$44.40
Purchase #3	$145.34	13.796%	$165.3911	$165.39	$165.40	$165.40
Purchase #4	$44.95	3.158%	$46.3695	$46.37	$46.35	$46.40
Purchase #5	$152.57	12.306%	$171.3453	$171.35	$171.35	$171.30
Purchase #6	$117.81	10.646%	$130.3521	$130.35	$130.35	$130.40
Purchase #7	$45.40	9.726%	$49.8156	$49.82	$49.80	$49.80
7 purchase totals =	$794.42		$871.8448	$871.86	$871.85	$871.90