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	$71.70	12.332%	$80.542	$80.54	$80.55	$80.50
Purchase #2	$55.59	8.678%	$60.4141	$60.41	$60.40	$60.40
Purchase #3	$234.74	3.651%	$243.3104	$243.31	$243.30	$243.30
Purchase #4	$75.95	3.853%	$78.8764	$78.88	$78.90	$78.90
Purchase #5	$85.33	3.675%	$88.4659	$88.47	$88.45	$88.50
Purchase #6	$234.38	4.596%	$245.1521	$245.15	$245.15	$245.20
Purchase #7	$17.55	10.868%	$19.4573	$19.46	$19.45	$19.50
7 purchase totals =	$775.24		$816.2182	$816.22	$816.20	$816.30