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	$203.56	9.440%	$222.7761	$222.78	$222.80	$222.80
Purchase #2	$132.94	13.233%	$150.532	$150.53	$150.55	$150.50
Purchase #3	$84.71	6.575%	$90.2797	$90.28	$90.30	$90.30
Purchase #4	$114.59	11.656%	$127.9466	$127.95	$127.95	$127.90
Purchase #5	$181.32	7.649%	$195.1892	$195.19	$195.20	$195.20
Purchase #6	$102.93	6.242%	$109.3549	$109.35	$109.35	$109.40
Purchase #7	$184.28	9.726%	$202.2031	$202.20	$202.20	$202.20
7 purchase totals =	$1,004.33		$1,098.2816	$1,098.28	$1,098.35	$1,098.30