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	$77.56	13.808%	$88.2695	$88.27	$88.25	$88.30
Purchase #2	$77.52	6.609%	$82.6433	$82.64	$82.65	$82.60
Purchase #3	$100.67	9.501%	$110.2347	$110.23	$110.25	$110.20
Purchase #4	$184.90	12.857%	$208.6726	$208.67	$208.65	$208.70
Purchase #5	$80.89	5.128%	$85.038	$85.04	$85.05	$85.00
Purchase #6	$215.41	10.785%	$238.642	$238.64	$238.65	$238.60
Purchase #7	$12.52	11.165%	$13.9179	$13.92	$13.90	$13.90
7 purchase totals =	$749.47		$827.4180	$827.41	$827.40	$827.30