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	$80.44	11.343%	$89.5643	$89.56	$89.55	$89.60
Purchase #2	$55.50	3.309%	$57.3365	$57.34	$57.35	$57.30
Purchase #3	$119.41	10.373%	$131.7964	$131.80	$131.80	$131.80
Purchase #4	$216.33	8.160%	$233.9825	$233.98	$234.00	$234.00
Purchase #5	$141.36	13.610%	$160.5991	$160.60	$160.60	$160.60
Purchase #6	$149.75	12.653%	$168.6979	$168.70	$168.70	$168.70
Purchase #7	$31.89	8.514%	$34.6051	$34.61	$34.60	$34.60
7 purchase totals =	$794.68		$876.5818	$876.59	$876.60	$876.60