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	$86.90	3.735%	$90.1457	$90.15	$90.15	$90.10
Purchase #2	$44.31	13.475%	$50.2808	$50.28	$50.30	$50.30
Purchase #3	$219.90	11.507%	$245.2039	$245.20	$245.20	$245.20
Purchase #4	$92.70	4.549%	$96.9169	$96.92	$96.90	$96.90
Purchase #5	$152.95	12.405%	$171.9234	$171.92	$171.90	$171.90
Purchase #6	$196.37	5.223%	$206.6264	$206.63	$206.65	$206.60
Purchase #7	$145.92	8.824%	$158.796	$158.80	$158.80	$158.80
7 purchase totals =	$939.05		$1,019.8931	$1,019.90	$1,019.90	$1,019.80