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	$244.83	8.272%	$265.0823	$265.08	$265.10	$265.10
Purchase #2	$113.40	5.737%	$119.9058	$119.91	$119.90	$119.90
Purchase #3	$21.35	7.550%	$22.9619	$22.96	$22.95	$23.00
Purchase #4	$88.80	11.858%	$99.3299	$99.33	$99.35	$99.30
Purchase #5	$62.30	7.748%	$67.127	$67.13	$67.15	$67.10
Purchase #6	$90.35	10.289%	$99.6461	$99.65	$99.65	$99.60
Purchase #7	$155.27	4.277%	$161.9109	$161.91	$161.90	$161.90
7 purchase totals =	$776.30		$835.9639	$835.97	$836.00	$835.90