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	$67.44	3.172%	$69.5792	$69.58	$69.60	$69.60
Purchase #2	$233.80	10.371%	$258.0474	$258.05	$258.05	$258.00
Purchase #3	$199.96	11.107%	$222.1696	$222.17	$222.15	$222.20
Purchase #4	$117.37	9.577%	$128.6105	$128.61	$128.60	$128.60
Purchase #5	$228.77	7.190%	$245.2186	$245.22	$245.20	$245.20
Purchase #6	$79.88	12.124%	$89.5647	$89.56	$89.55	$89.60
Purchase #7	$153.74	9.284%	$168.0132	$168.01	$168.00	$168.00
7 purchase totals =	$1,080.96		$1,181.2032	$1,181.20	$1,181.15	$1,181.20