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	$82.58	9.225%	$90.198	$90.20	$90.20	$90.20
Purchase #2	$44.27	7.124%	$47.4238	$47.42	$47.40	$47.40
Purchase #3	$188.53	11.304%	$209.8414	$209.84	$209.85	$209.80
Purchase #4	$154.88	13.516%	$175.8136	$175.81	$175.80	$175.80
Purchase #5	$212.82	4.684%	$222.7885	$222.79	$222.80	$222.80
Purchase #6	$248.86	10.666%	$275.4034	$275.40	$275.40	$275.40
Purchase #7	$156.84	8.532%	$170.2216	$170.22	$170.20	$170.20
7 purchase totals =	$1,088.78		$1,191.6903	$1,191.68	$1,191.65	$1,191.60