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	$26.79	5.294%	$28.2083	$28.21	$28.20	$28.20
Purchase #2	$152.53	12.204%	$171.1448	$171.14	$171.15	$171.10
Purchase #3	$107.97	10.329%	$119.1222	$119.12	$119.10	$119.10
Purchase #4	$123.96	6.376%	$131.8637	$131.86	$131.85	$131.90
Purchase #5	$148.57	12.517%	$167.1665	$167.17	$167.15	$167.20
Purchase #6	$157.33	10.313%	$173.5554	$173.56	$173.55	$173.60
Purchase #7	$88.58	3.684%	$91.8433	$91.84	$91.85	$91.80
7 purchase totals =	$805.73		$882.9042	$882.90	$882.85	$882.90