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	$69.86	6.366%	$74.3073	$74.31	$74.30	$74.30
Purchase #2	$85.96	5.254%	$90.4763	$90.48	$90.50	$90.50
Purchase #3	$230.52	6.436%	$245.3563	$245.36	$245.35	$245.40
Purchase #4	$12.48	12.661%	$14.0601	$14.06	$14.05	$14.10
Purchase #5	$144.71	3.765%	$150.1583	$150.16	$150.15	$150.20
Purchase #6	$160.77	7.384%	$172.6413	$172.64	$172.65	$172.60
Purchase #7	$64.96	3.641%	$67.3252	$67.33	$67.35	$67.30
7 purchase totals =	$769.26		$814.3248	$814.34	$814.35	$814.40