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	$161.59	6.805%	$172.5862	$172.59	$172.60	$172.60
Purchase #2	$200.33	10.585%	$221.5349	$221.53	$221.55	$221.50
Purchase #3	$170.52	9.768%	$187.1764	$187.18	$187.20	$187.20
Purchase #4	$225.52	11.270%	$250.9361	$250.94	$250.95	$250.90
Purchase #5	$174.33	3.159%	$179.8371	$179.84	$179.85	$179.80
Purchase #6	$191.78	11.596%	$214.0188	$214.02	$214.00	$214.00
Purchase #7	$64.98	10.586%	$71.8588	$71.86	$71.85	$71.90
7 purchase totals =	$1,189.05		$1,297.9483	$1,297.96	$1,298.00	$1,297.90