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	$137.71	9.178%	$150.349	$150.35	$150.35	$150.30
Purchase #2	$90.87	6.550%	$96.822	$96.82	$96.80	$96.80
Purchase #3	$24.49	10.669%	$27.1028	$27.10	$27.10	$27.10
Purchase #4	$116.77	10.352%	$128.858	$128.86	$128.85	$128.90
Purchase #5	$226.82	10.265%	$250.1031	$250.10	$250.10	$250.10
Purchase #6	$189.52	11.268%	$210.8751	$210.88	$210.90	$210.90
Purchase #7	$147.47	10.104%	$162.3704	$162.37	$162.35	$162.40
7 purchase totals =	$933.65		$1,026.4804	$1,026.48	$1,026.45	$1,026.50