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	$41.72	13.171%	$47.2149	$47.21	$47.20	$47.20
Purchase #2	$59.25	10.566%	$65.5104	$65.51	$65.50	$65.50
Purchase #3	$160.56	5.188%	$168.8899	$168.89	$168.90	$168.90
Purchase #4	$60.36	13.769%	$68.671	$68.67	$68.65	$68.70
Purchase #5	$52.94	4.721%	$55.4393	$55.44	$55.45	$55.40
Purchase #6	$217.33	6.390%	$231.2174	$231.22	$231.20	$231.20
Purchase #7	$186.73	7.401%	$200.5499	$200.55	$200.55	$200.50
7 purchase totals =	$778.89		$837.4928	$837.49	$837.45	$837.40