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	$116.38	12.131%	$130.4981	$130.50	$130.50	$130.50
Purchase #2	$219.51	10.842%	$243.3093	$243.31	$243.30	$243.30
Purchase #3	$12.56	9.509%	$13.7543	$13.75	$13.75	$13.80
Purchase #4	$131.96	11.718%	$147.4231	$147.42	$147.40	$147.40
Purchase #5	$155.98	11.835%	$174.4402	$174.44	$174.45	$174.40
Purchase #6	$81.46	9.854%	$89.4871	$89.49	$89.50	$89.50
Purchase #7	$172.61	3.127%	$178.0075	$178.01	$178.00	$178.00
7 purchase totals =	$890.46		$976.9196	$976.92	$976.90	$976.90