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	$28.25	9.729%	$30.9984	$31.00	$31.00	$31.00
Purchase #2	$33.32	10.647%	$36.8676	$36.87	$36.85	$36.90
Purchase #3	$180.84	9.653%	$198.2965	$198.30	$198.30	$198.30
Purchase #4	$188.52	6.227%	$200.2591	$200.26	$200.25	$200.30
Purchase #5	$198.83	11.804%	$222.2999	$222.30	$222.30	$222.30
Purchase #6	$205.35	9.801%	$225.4764	$225.48	$225.50	$225.50
Purchase #7	$203.89	12.835%	$230.0593	$230.06	$230.05	$230.10
7 purchase totals =	$1,039.00		$1,144.2572	$1,144.27	$1,144.25	$1,144.40