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	$130.62	7.121%	$139.9215	$139.92	$139.90	$139.90
Purchase #2	$196.62	9.768%	$215.8258	$215.83	$215.85	$215.80
Purchase #3	$12.29	9.166%	$13.4165	$13.42	$13.40	$13.40
Purchase #4	$80.65	11.443%	$89.8788	$89.88	$89.90	$89.90
Purchase #5	$94.37	12.718%	$106.372	$106.37	$106.35	$106.40
Purchase #6	$153.92	5.644%	$162.6072	$162.61	$162.60	$162.60
Purchase #7	$93.43	7.869%	$100.782	$100.78	$100.80	$100.80
7 purchase totals =	$761.90		$828.8038	$828.81	$828.80	$828.80