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	$233.25	5.379%	$245.7965	$245.80	$245.80	$245.80
Purchase #2	$108.53	7.285%	$116.4364	$116.44	$116.45	$116.40
Purchase #3	$99.40	11.567%	$110.8976	$110.90	$110.90	$110.90
Purchase #4	$233.65	12.830%	$263.6273	$263.63	$263.65	$263.60
Purchase #5	$72.34	8.464%	$78.4629	$78.46	$78.45	$78.50
Purchase #6	$213.29	12.621%	$240.2093	$240.21	$240.20	$240.20
Purchase #7	$205.36	10.756%	$227.4485	$227.45	$227.45	$227.40
7 purchase totals =	$1,165.82		$1,282.8785	$1,282.89	$1,282.90	$1,282.80