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	$6.72	7.839%	$7.2468	$7.25	$7.25	$7.20
Purchase #2	$135.35	9.664%	$148.4302	$148.43	$148.45	$148.40
Purchase #3	$52.29	7.676%	$56.3038	$56.30	$56.30	$56.30
Purchase #4	$44.52	5.130%	$46.8039	$46.80	$46.80	$46.80
Purchase #5	$237.83	9.528%	$260.4904	$260.49	$260.50	$260.50
Purchase #6	$185.52	13.674%	$210.888	$210.89	$210.90	$210.90
Purchase #7	$85.59	13.102%	$96.804	$96.80	$96.80	$96.80
7 purchase totals =	$747.82		$826.9671	$826.96	$827.00	$826.90