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	$71.29	13.653%	$81.0232	$81.02	$81.00	$81.00
Purchase #2	$221.32	13.372%	$250.9149	$250.91	$250.90	$250.90
Purchase #3	$70.74	13.856%	$80.5417	$80.54	$80.55	$80.50
Purchase #4	$101.61	11.432%	$113.2261	$113.23	$113.25	$113.20
Purchase #5	$55.83	10.859%	$61.8926	$61.89	$61.90	$61.90
Purchase #6	$150.53	10.197%	$165.8795	$165.88	$165.90	$165.90
Purchase #7	$109.52	3.481%	$113.3324	$113.33	$113.35	$113.30
7 purchase totals =	$780.84		$866.8104	$866.80	$866.85	$866.70