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	$29.67	9.618%	$32.5237	$32.52	$32.50	$32.50
Purchase #2	$56.88	5.317%	$59.9043	$59.90	$59.90	$59.90
Purchase #3	$226.58	12.555%	$255.0271	$255.03	$255.05	$255.00
Purchase #4	$182.29	7.278%	$195.5571	$195.56	$195.55	$195.60
Purchase #5	$64.86	3.646%	$67.2248	$67.22	$67.20	$67.20
Purchase #6	$75.43	3.443%	$78.0271	$78.03	$78.05	$78.00
Purchase #7	$191.53	9.642%	$209.9973	$210.00	$210.00	$210.00
7 purchase totals =	$827.24		$898.2614	$898.26	$898.25	$898.20