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	$13.55	11.639%	$15.1271	$15.13	$15.15	$15.10
Purchase #2	$53.79	10.260%	$59.3089	$59.31	$59.30	$59.30
Purchase #3	$119.84	11.697%	$133.8577	$133.86	$133.85	$133.90
Purchase #4	$37.67	13.731%	$42.8425	$42.84	$42.85	$42.80
Purchase #5	$144.39	3.467%	$149.396	$149.40	$149.40	$149.40
Purchase #6	$145.41	11.541%	$162.1918	$162.19	$162.20	$162.20
Purchase #7	$85.54	5.414%	$90.1711	$90.17	$90.15	$90.20
7 purchase totals =	$600.19		$652.8951	$652.90	$652.90	$652.90