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	$39.37	12.252%	$44.1936	$44.19	$44.20	$44.20
Purchase #2	$30.63	3.846%	$31.808	$31.81	$31.80	$31.80
Purchase #3	$193.83	12.784%	$218.6092	$218.61	$218.60	$218.60
Purchase #4	$240.79	11.443%	$268.3436	$268.34	$268.35	$268.30
Purchase #5	$232.82	6.736%	$248.5028	$248.50	$248.50	$248.50
Purchase #6	$95.77	7.441%	$102.8962	$102.90	$102.90	$102.90
Purchase #7	$80.76	10.601%	$89.3214	$89.32	$89.30	$89.30
7 purchase totals =	$913.97		$1,003.6748	$1,003.67	$1,003.65	$1,003.60