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	$144.82	3.615%	$150.0552	$150.06	$150.05	$150.10
Purchase #2	$115.49	4.296%	$120.4515	$120.45	$120.45	$120.50
Purchase #3	$18.85	11.681%	$21.0519	$21.05	$21.05	$21.10
Purchase #4	$205.61	3.165%	$212.1176	$212.12	$212.10	$212.10
Purchase #5	$227.27	11.643%	$253.731	$253.73	$253.75	$253.70
Purchase #6	$27.43	4.189%	$28.579	$28.58	$28.60	$28.60
Purchase #7	$67.71	6.511%	$72.1186	$72.12	$72.10	$72.10
7 purchase totals =	$807.18		$858.1048	$858.11	$858.10	$858.20