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	$119.30	10.310%	$131.5998	$131.60	$131.60	$131.60
Purchase #2	$145.35	3.524%	$150.4721	$150.47	$150.45	$150.50
Purchase #3	$26.30	9.824%	$28.8837	$28.88	$28.90	$28.90
Purchase #4	$93.96	5.749%	$99.3618	$99.36	$99.35	$99.40
Purchase #5	$51.59	7.775%	$55.6011	$55.60	$55.60	$55.60
Purchase #6	$118.89	8.455%	$128.9421	$128.94	$128.95	$128.90
Purchase #7	$176.48	10.135%	$194.3662	$194.37	$194.35	$194.40
7 purchase totals =	$731.87		$789.2268	$789.22	$789.20	$789.30