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	$160.82	12.659%	$181.1782	$181.18	$181.20	$181.20
Purchase #2	$95.50	11.853%	$106.8196	$106.82	$106.80	$106.80
Purchase #3	$150.26	13.711%	$170.8621	$170.86	$170.85	$170.90
Purchase #4	$101.34	6.873%	$108.3051	$108.31	$108.30	$108.30
Purchase #5	$236.52	7.190%	$253.5258	$253.53	$253.55	$253.50
Purchase #6	$68.98	13.297%	$78.1523	$78.15	$78.15	$78.20
Purchase #7	$145.31	13.637%	$165.1259	$165.13	$165.15	$165.10
7 purchase totals =	$958.73		$1,063.9690	$1,063.98	$1,064.00	$1,064.00