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	$132.58	13.738%	$150.7938	$150.79	$150.80	$150.80
Purchase #2	$186.86	4.296%	$194.8875	$194.89	$194.90	$194.90
Purchase #3	$162.82	12.258%	$182.7785	$182.78	$182.80	$182.80
Purchase #4	$204.34	10.208%	$225.199	$225.20	$225.20	$225.20
Purchase #5	$134.27	10.586%	$148.4838	$148.48	$148.50	$148.50
Purchase #6	$112.64	3.724%	$116.8347	$116.83	$116.85	$116.80
Purchase #7	$98.61	10.823%	$109.2826	$109.28	$109.30	$109.30
7 purchase totals =	$1,032.12		$1,128.2599	$1,128.25	$1,128.35	$1,128.30