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	$37.36	13.431%	$42.3778	$42.38	$42.40	$42.40
Purchase #2	$86.86	3.622%	$90.0061	$90.01	$90.00	$90.00
Purchase #3	$247.30	13.850%	$281.5511	$281.55	$281.55	$281.60
Purchase #4	$140.55	9.842%	$154.3829	$154.38	$154.40	$154.40
Purchase #5	$93.27	4.740%	$97.691	$97.69	$97.70	$97.70
Purchase #6	$238.93	4.644%	$250.0259	$250.03	$250.05	$250.00
Purchase #7	$216.86	3.322%	$224.0641	$224.06	$224.05	$224.10
7 purchase totals =	$1,061.13		$1,140.0989	$1,140.10	$1,140.15	$1,140.20