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	$15.84	3.119%	$16.334	$16.33	$16.35	$16.30
Purchase #2	$57.95	8.357%	$62.7929	$62.79	$62.80	$62.80
Purchase #3	$126.72	11.667%	$141.5044	$141.50	$141.50	$141.50
Purchase #4	$84.96	6.231%	$90.2539	$90.25	$90.25	$90.30
Purchase #5	$66.94	8.623%	$72.7122	$72.71	$72.70	$72.70
Purchase #6	$28.77	6.657%	$30.6852	$30.69	$30.70	$30.70
Purchase #7	$210.50	3.793%	$218.4843	$218.48	$218.50	$218.50
7 purchase totals =	$591.68		$632.7669	$632.75	$632.80	$632.80