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	$63.53	10.706%	$70.3315	$70.33	$70.35	$70.30
Purchase #2	$181.82	10.720%	$201.3111	$201.31	$201.30	$201.30
Purchase #3	$19.47	12.544%	$21.9123	$21.91	$21.90	$21.90
Purchase #4	$76.98	8.654%	$83.6418	$83.64	$83.65	$83.60
Purchase #5	$18.96	11.606%	$21.1605	$21.16	$21.15	$21.20
Purchase #6	$61.56	12.521%	$69.2679	$69.27	$69.25	$69.30
Purchase #7	$189.84	5.441%	$200.1692	$200.17	$200.15	$200.20
7 purchase totals =	$612.16		$667.7943	$667.79	$667.75	$667.80