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	$17.78	6.490%	$18.9339	$18.93	$18.95	$18.90
Purchase #2	$159.58	9.616%	$174.9252	$174.93	$174.95	$174.90
Purchase #3	$166.56	3.737%	$172.7843	$172.78	$172.80	$172.80
Purchase #4	$240.44	6.199%	$255.3449	$255.34	$255.35	$255.30
Purchase #5	$153.71	9.197%	$167.8467	$167.85	$167.85	$167.80
Purchase #6	$33.32	7.424%	$35.7937	$35.79	$35.80	$35.80
Purchase #7	$51.36	4.618%	$53.7318	$53.73	$53.75	$53.70
7 purchase totals =	$822.75		$879.3605	$879.35	$879.45	$879.20