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	$74.80	12.585%	$84.2136	$84.21	$84.20	$84.20
Purchase #2	$50.74	5.535%	$53.5485	$53.55	$53.55	$53.50
Purchase #3	$87.69	3.313%	$90.5952	$90.60	$90.60	$90.60
Purchase #4	$27.78	7.288%	$29.8046	$29.80	$29.80	$29.80
Purchase #5	$147.86	13.280%	$167.4958	$167.50	$167.50	$167.50
Purchase #6	$229.64	6.825%	$245.3129	$245.31	$245.30	$245.30
Purchase #7	$154.32	8.168%	$166.9249	$166.92	$166.90	$166.90
7 purchase totals =	$772.83		$837.8955	$837.89	$837.85	$837.80