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	$238.40	13.591%	$270.8009	$270.80	$270.80	$270.80
Purchase #2	$176.41	3.245%	$182.1345	$182.13	$182.15	$182.10
Purchase #3	$132.93	13.521%	$150.9035	$150.90	$150.90	$150.90
Purchase #4	$99.69	6.120%	$105.791	$105.79	$105.80	$105.80
Purchase #5	$14.76	3.681%	$15.3033	$15.30	$15.30	$15.30
Purchase #6	$154.58	8.800%	$168.183	$168.18	$168.20	$168.20
Purchase #7	$139.45	9.564%	$152.787	$152.79	$152.80	$152.80
7 purchase totals =	$956.22		$1,045.9032	$1,045.89	$1,045.95	$1,045.90