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	$204.59	9.712%	$224.4598	$224.46	$224.45	$224.50
Purchase #2	$142.69	10.373%	$157.4912	$157.49	$157.50	$157.50
Purchase #3	$57.76	12.337%	$64.8859	$64.89	$64.90	$64.90
Purchase #4	$240.36	7.434%	$258.2284	$258.23	$258.25	$258.20
Purchase #5	$180.71	10.796%	$200.2195	$200.22	$200.20	$200.20
Purchase #6	$57.29	12.187%	$64.2719	$64.27	$64.25	$64.30
Purchase #7	$87.58	3.615%	$90.746	$90.75	$90.75	$90.70
7 purchase totals =	$970.98		$1,060.3027	$1,060.31	$1,060.30	$1,060.30