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	$70.56	3.337%	$72.9146	$72.91	$72.90	$72.90
Purchase #2	$31.59	8.533%	$34.2856	$34.29	$34.30	$34.30
Purchase #3	$229.94	12.847%	$259.4804	$259.48	$259.50	$259.50
Purchase #4	$218.87	11.156%	$243.2871	$243.29	$243.30	$243.30
Purchase #5	$109.33	4.359%	$114.0957	$114.10	$114.10	$114.10
Purchase #6	$192.56	7.441%	$206.8884	$206.89	$206.90	$206.90
Purchase #7	$171.30	9.566%	$187.6866	$187.69	$187.70	$187.70
7 purchase totals =	$1,024.15		$1,118.6384	$1,118.65	$1,118.70	$1,118.70