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	$210.28	13.471%	$238.6068	$238.61	$238.60	$238.60
Purchase #2	$129.87	12.266%	$145.7999	$145.80	$145.80	$145.80
Purchase #3	$87.48	4.502%	$91.4183	$91.42	$91.40	$91.40
Purchase #4	$201.69	10.801%	$223.4745	$223.47	$223.45	$223.50
Purchase #5	$25.92	12.858%	$29.2528	$29.25	$29.25	$29.30
Purchase #6	$225.82	5.628%	$238.5291	$238.53	$238.55	$238.50
Purchase #7	$61.43	5.371%	$64.7294	$64.73	$64.75	$64.70
7 purchase totals =	$942.49		$1,031.8108	$1,031.81	$1,031.80	$1,031.80