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	$57.96	5.250%	$61.0029	$61.00	$61.00	$61.00
Purchase #2	$73.30	7.691%	$78.9375	$78.94	$78.95	$78.90
Purchase #3	$203.61	12.803%	$229.6782	$229.68	$229.70	$229.70
Purchase #4	$12.50	3.690%	$12.9613	$12.96	$12.95	$13.00
Purchase #5	$178.31	6.678%	$190.2175	$190.22	$190.20	$190.20
Purchase #6	$202.79	9.113%	$221.2703	$221.27	$221.25	$221.30
Purchase #7	$67.69	3.507%	$70.0639	$70.06	$70.05	$70.10
7 purchase totals =	$796.16		$864.1316	$864.13	$864.10	$864.20