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	$40.96	10.362%	$45.2043	$45.20	$45.20	$45.20
Purchase #2	$179.40	8.630%	$194.8822	$194.88	$194.90	$194.90
Purchase #3	$100.76	11.621%	$112.4693	$112.47	$112.45	$112.50
Purchase #4	$101.37	3.330%	$104.7456	$104.75	$104.75	$104.70
Purchase #5	$220.79	9.609%	$242.0057	$242.01	$242.00	$242.00
Purchase #6	$94.80	12.299%	$106.4595	$106.46	$106.45	$106.50
Purchase #7	$80.41	5.844%	$85.1092	$85.11	$85.10	$85.10
7 purchase totals =	$818.49		$890.8758	$890.88	$890.85	$890.90