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	$30.57	11.663%	$34.1354	$34.14	$34.15	$34.10
Purchase #2	$181.39	8.516%	$196.8372	$196.84	$196.85	$196.80
Purchase #3	$79.56	13.689%	$90.451	$90.45	$90.45	$90.50
Purchase #4	$218.77	13.513%	$248.3324	$248.33	$248.35	$248.30
Purchase #5	$70.64	7.407%	$75.8723	$75.87	$75.85	$75.90
Purchase #6	$150.86	11.739%	$168.5695	$168.57	$168.55	$168.60
Purchase #7	$95.84	11.511%	$106.8721	$106.87	$106.85	$106.90
7 purchase totals =	$827.63		$921.0699	$921.07	$921.05	$921.10