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	$233.28	11.532%	$260.1818	$260.18	$260.20	$260.20
Purchase #2	$73.30	10.349%	$80.8858	$80.89	$80.90	$80.90
Purchase #3	$148.61	6.124%	$157.7109	$157.71	$157.70	$157.70
Purchase #4	$53.90	10.137%	$59.3638	$59.36	$59.35	$59.40
Purchase #5	$57.65	3.277%	$59.5392	$59.54	$59.55	$59.50
Purchase #6	$70.88	10.739%	$78.4918	$78.49	$78.50	$78.50
Purchase #7	$218.48	3.452%	$226.0219	$226.02	$226.00	$226.00
7 purchase totals =	$856.10		$922.1952	$922.19	$922.20	$922.20