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	$170.56	12.507%	$191.8919	$191.89	$191.90	$191.90
Purchase #2	$19.47	13.394%	$22.0778	$22.08	$22.10	$22.10
Purchase #3	$203.70	9.135%	$222.308	$222.31	$222.30	$222.30
Purchase #4	$84.88	5.587%	$89.6222	$89.62	$89.60	$89.60
Purchase #5	$245.86	4.148%	$256.0583	$256.06	$256.05	$256.10
Purchase #6	$10.52	4.372%	$10.9799	$10.98	$11.00	$11.00
Purchase #7	$64.52	8.556%	$70.0403	$70.04	$70.05	$70.00
7 purchase totals =	$799.51		$862.9784	$862.98	$863.00	$863.00