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	$124.64	11.193%	$138.591	$138.59	$138.60	$138.60
Purchase #2	$62.62	7.814%	$67.5131	$67.51	$67.50	$67.50
Purchase #3	$18.56	10.279%	$20.4678	$20.47	$20.45	$20.50
Purchase #4	$250.73	11.409%	$279.3358	$279.34	$279.35	$279.30
Purchase #5	$229.34	5.646%	$242.2885	$242.29	$242.30	$242.30
Purchase #6	$94.25	3.228%	$97.2924	$97.29	$97.30	$97.30
Purchase #7	$169.28	9.526%	$185.4056	$185.41	$185.40	$185.40
7 purchase totals =	$949.42		$1,030.8942	$1,030.90	$1,030.90	$1,030.90