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	$243.33	13.326%	$275.7562	$275.76	$275.75	$275.80
Purchase #2	$27.52	3.590%	$28.508	$28.51	$28.50	$28.50
Purchase #3	$165.82	13.250%	$187.7912	$187.79	$187.80	$187.80
Purchase #4	$215.60	4.582%	$225.4788	$225.48	$225.50	$225.50
Purchase #5	$104.58	6.837%	$111.7301	$111.73	$111.75	$111.70
Purchase #6	$140.40	3.115%	$144.7735	$144.77	$144.75	$144.80
Purchase #7	$160.95	6.219%	$170.9595	$170.96	$170.95	$171.00
7 purchase totals =	$1,058.20		$1,144.9973	$1,145.00	$1,145.00	$1,145.10