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	$162.87	9.739%	$178.7319	$178.73	$178.75	$178.70
Purchase #2	$120.72	12.751%	$136.113	$136.11	$136.10	$136.10
Purchase #3	$110.45	11.869%	$123.5593	$123.56	$123.55	$123.60
Purchase #4	$201.39	9.558%	$220.6389	$220.64	$220.65	$220.60
Purchase #5	$226.71	11.667%	$253.1603	$253.16	$253.15	$253.20
Purchase #6	$173.94	6.549%	$185.3313	$185.33	$185.35	$185.30
Purchase #7	$81.37	13.465%	$92.3265	$92.33	$92.35	$92.30
7 purchase totals =	$1,077.45		$1,189.8612	$1,189.86	$1,189.90	$1,189.80