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	$128.51	7.214%	$137.7807	$137.78	$137.80	$137.80
Purchase #2	$159.35	12.557%	$179.3596	$179.36	$179.35	$179.40
Purchase #3	$85.43	6.227%	$90.7497	$90.75	$90.75	$90.70
Purchase #4	$129.63	9.658%	$142.1497	$142.15	$142.15	$142.10
Purchase #5	$17.62	3.367%	$18.2133	$18.21	$18.20	$18.20
Purchase #6	$181.56	4.448%	$189.6358	$189.64	$189.65	$189.60
Purchase #7	$218.53	3.133%	$225.3765	$225.38	$225.40	$225.40
7 purchase totals =	$920.63		$983.2653	$983.27	$983.30	$983.20