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	$82.78	10.303%	$91.3088	$91.31	$91.30	$91.30
Purchase #2	$153.72	8.769%	$167.1997	$167.20	$167.20	$167.20
Purchase #3	$115.73	4.197%	$120.5872	$120.59	$120.60	$120.60
Purchase #4	$237.60	10.669%	$262.9495	$262.95	$262.95	$262.90
Purchase #5	$188.51	11.214%	$209.6495	$209.65	$209.65	$209.60
Purchase #6	$81.33	9.459%	$89.023	$89.02	$89.00	$89.00
Purchase #7	$168.85	4.427%	$176.325	$176.33	$176.35	$176.30
7 purchase totals =	$1,028.52		$1,117.0427	$1,117.05	$1,117.05	$1,116.90