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	$36.90	12.599%	$41.549	$41.55	$41.55	$41.50
Purchase #2	$40.93	3.259%	$42.2639	$42.26	$42.25	$42.30
Purchase #3	$134.69	12.787%	$151.9128	$151.91	$151.90	$151.90
Purchase #4	$178.78	13.225%	$202.4237	$202.42	$202.40	$202.40
Purchase #5	$57.49	3.201%	$59.3303	$59.33	$59.35	$59.30
Purchase #6	$196.31	10.425%	$216.7753	$216.78	$216.80	$216.80
Purchase #7	$242.98	9.354%	$265.7083	$265.71	$265.70	$265.70
7 purchase totals =	$888.08		$979.9633	$979.96	$979.95	$979.90