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	$103.33	7.758%	$111.3463	$111.35	$111.35	$111.30
Purchase #2	$85.91	4.432%	$89.7175	$89.72	$89.70	$89.70
Purchase #3	$30.88	8.165%	$33.4014	$33.40	$33.40	$33.40
Purchase #4	$161.61	4.528%	$168.9277	$168.93	$168.95	$168.90
Purchase #5	$113.69	9.262%	$124.22	$124.22	$124.20	$124.20
Purchase #6	$48.99	8.153%	$52.9842	$52.98	$53.00	$53.00
Purchase #7	$31.48	13.644%	$35.7751	$35.78	$35.80	$35.80
7 purchase totals =	$575.89		$616.3722	$616.38	$616.40	$616.30