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	$146.85	12.843%	$165.7099	$165.71	$165.70	$165.70
Purchase #2	$168.90	11.262%	$187.9215	$187.92	$187.90	$187.90
Purchase #3	$86.73	8.590%	$94.1801	$94.18	$94.20	$94.20
Purchase #4	$6.77	10.312%	$7.4681	$7.47	$7.45	$7.50
Purchase #5	$82.25	7.520%	$88.4352	$88.44	$88.45	$88.40
Purchase #6	$31.46	6.288%	$33.4382	$33.44	$33.45	$33.40
Purchase #7	$109.52	7.289%	$117.5029	$117.50	$117.50	$117.50
7 purchase totals =	$632.48		$694.6559	$694.66	$694.65	$694.60