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	$118.36	7.559%	$127.3068	$127.31	$127.30	$127.30
Purchase #2	$20.60	3.442%	$21.3091	$21.31	$21.30	$21.30
Purchase #3	$213.57	9.860%	$234.628	$234.63	$234.65	$234.60
Purchase #4	$209.74	11.315%	$233.4721	$233.47	$233.45	$233.50
Purchase #5	$93.27	11.872%	$104.343	$104.34	$104.35	$104.30
Purchase #6	$27.43	4.183%	$28.5774	$28.58	$28.60	$28.60
Purchase #7	$81.95	9.867%	$90.036	$90.04	$90.05	$90.00
7 purchase totals =	$764.92		$839.6724	$839.68	$839.70	$839.60