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	$238.41	10.862%	$264.3061	$264.31	$264.30	$264.30
Purchase #2	$244.85	12.440%	$275.3093	$275.31	$275.30	$275.30
Purchase #3	$245.52	3.658%	$254.5011	$254.50	$254.50	$254.50
Purchase #4	$71.53	8.127%	$77.3432	$77.34	$77.35	$77.30
Purchase #5	$170.57	13.867%	$194.2229	$194.22	$194.20	$194.20
Purchase #6	$250.69	4.172%	$261.1488	$261.15	$261.15	$261.10
Purchase #7	$246.88	9.534%	$270.4175	$270.42	$270.40	$270.40
7 purchase totals =	$1,468.45		$1,597.2489	$1,597.25	$1,597.20	$1,597.10