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	$42.65	7.359%	$45.7886	$45.79	$45.80	$45.80
Purchase #2	$121.56	4.786%	$127.3779	$127.38	$127.40	$127.40
Purchase #3	$81.69	10.149%	$89.9807	$89.98	$90.00	$90.00
Purchase #4	$245.73	6.687%	$262.162	$262.16	$262.15	$262.20
Purchase #5	$79.73	11.166%	$88.6327	$88.63	$88.65	$88.60
Purchase #6	$104.87	9.503%	$114.8358	$114.84	$114.85	$114.80
Purchase #7	$84.72	6.110%	$89.8964	$89.90	$89.90	$89.90
7 purchase totals =	$760.95		$818.6741	$818.68	$818.75	$818.70