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	$234.60	6.687%	$250.2877	$250.29	$250.30	$250.30
Purchase #2	$87.46	13.570%	$99.3283	$99.33	$99.35	$99.30
Purchase #3	$170.74	8.482%	$185.2222	$185.22	$185.20	$185.20
Purchase #4	$123.96	6.345%	$131.8253	$131.83	$131.85	$131.80
Purchase #5	$40.82	6.549%	$43.4933	$43.49	$43.50	$43.50
Purchase #6	$121.69	3.614%	$126.0879	$126.09	$126.10	$126.10
Purchase #7	$108.62	3.780%	$112.7258	$112.73	$112.75	$112.70
7 purchase totals =	$887.89		$948.9705	$948.98	$949.05	$948.90