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	$148.76	6.764%	$158.8221	$158.82	$158.80	$158.80
Purchase #2	$102.34	3.480%	$105.9014	$105.90	$105.90	$105.90
Purchase #3	$164.31	3.661%	$170.3254	$170.33	$170.35	$170.30
Purchase #4	$44.53	12.739%	$50.2027	$50.20	$50.20	$50.20
Purchase #5	$79.37	13.225%	$89.8667	$89.87	$89.85	$89.90
Purchase #6	$244.75	13.350%	$277.4241	$277.42	$277.40	$277.40
Purchase #7	$93.74	4.652%	$98.1008	$98.10	$98.10	$98.10
7 purchase totals =	$877.80		$950.6432	$950.64	$950.60	$950.60