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	$221.54	13.207%	$250.7988	$250.80	$250.80	$250.80
Purchase #2	$80.92	4.172%	$84.296	$84.30	$84.30	$84.30
Purchase #3	$193.96	13.590%	$220.3192	$220.32	$220.30	$220.30
Purchase #4	$100.86	12.499%	$113.4665	$113.47	$113.45	$113.50
Purchase #5	$31.83	8.241%	$34.4531	$34.45	$34.45	$34.50
Purchase #6	$223.85	4.460%	$233.8337	$233.83	$233.85	$233.80
Purchase #7	$79.79	12.369%	$89.6592	$89.66	$89.65	$89.70
7 purchase totals =	$932.75		$1,026.8265	$1,026.83	$1,026.80	$1,026.90